Surface acoustic wave device and environmental difference detecting apparatus using the surface acoustic wave device

ABSTRACT

A surface acoustic wave device includes a three-dimensional substrate having an annular curved surface enabling to propagate a surface acoustic wave, and an electro-acoustic transducing element, which excites and propagates the surface wave along the surface, and receives the propagated surface wave. The substrate is made of a Li 2 B 4 O 7 , Bi 12 SiO 20 , LiNbO 3 , LiTaO 3 , or quartz crystal, and the element propagates the surface wave along a line of intersection between a crystal face of the crystal and the surface, and the line of intersection is defined as an outermost circumferential line of the surface. An environmental difference detecting apparatus uses the device having a plurality of propagating surface zones and compares surface acoustic wave reception signals of electro-acoustic transducing elements in the propagating surface zones of the device with each other, and detects an environmental difference in space portions with which the propagating surface zones come into contact.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 11/377,615filed Mar. 17, 2006, pending, which is a continuation application of PCTapplication no. PCT/JP2004/013755, filed Sep. 21, 2004, which is basedupon and claims the benefit of priority from prior Japanese patentapplications no. 2003-327950, filed Sep. 19, 2003; and no. 2003-327951,filed Sep. 19, 2003, the entire contents of the foregoing beingincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface acoustic wave device, and anenvironmental difference detecting apparatus using the surface acousticwave device.

2. Description of the Related Art

Conventionally, there is well known a surface acoustic wave devicecomprising: a substrate having a surface capable of exciting a surfaceacoustic wave (SAW) and propagating the excited surface acoustic wave:and an electro-acoustic transducing element capable of exciting thesurface acoustic wave along a surface of the substrate, propagating thesurface acoustic wave along the surface, and receiving the propagatedsurface acoustic wave.

A surface acoustic device is used as a delay line, an oscillatingdevice, a resonating device, a frequency selecting device, a variety ofsensors including, for example, a chemical sensor, a biological sensorand a pressure sensor, or a remote tag, etc.

International Publication WO 01/45255 discloses a spherically shapedsurface acoustic wave device. A substrate of the spherically shapedsurface acoustic device has a spherically shaped surface capable ofexciting a surface acoustic wave and propagating the excited surfaceacoustic wave. An electro-acoustic transducing element of thespherically shaped surface acoustic wave device is arranged in a bandshaped zone having a predetermined width and being continuous in anannular shape on the spherically shaped surface of the substrate. Theelectro-acoustic transducing element is configured to propagate thesurface acoustic wave excited along the surface in a direction in whichthe band shaped zone is continuous, and to repeatedly circulate thepropagated wave.

The spherically shaped surface acoustic wave device can repeatedlycirculate the surface acoustic wave, which is excited by theelectro-acoustic transducing element in the band shaped surface acousticwave propagating zone of the substrate that is continuous in the annularshape, in the band shaped zone without substantially attenuating thesurface acoustic wave.

In order to propagate a surface acoustic wave along a surface of asubstrate of a surface acoustic wave device, the whole substrate is madeof a material capable of being excited to generate a surface acousticwave and capable of propagating the excited surface acoustic wave, oralternatively is made by adhering a thin film, which is formed of amaterial capable of being excited and propagating a surface acousticwave, on its surface.

It is known that the substrate formed of a combination with the thinfilm is high in manufacturing cost and is unsuitable for amass-production at the present stage. It is also known that, in thesubstrate formed of only the material capable of being excited andpropagating the surface acoustic wave, a difference occurs in aperformance of propagating the surface acoustic wave such that thesurface acoustic wave cannot be propagated or circulated depending on adirection in which an attempt is made to propagate the surface acousticwave. Along the surface, it is difficult to propagate or circulate thesurface acoustic wave in a plurality of different directions from eachother.

The present invention has been made under the above-describedcircumstances, and an object of the present invention is to provide asurface acoustic wave device suitable to a mass-production and capableof always stably achieving a good surface acoustic wave propagationperformance, and an environmental difference detecting apparatus usingthe surface acoustic wave device.

BRIEF SUMMARY OF THE INVENTION

In order to achieve the above described object, a surface acoustic wavedevice according to this invention comprises:

a three-dimensional substrate having a surface, which includes at leasta part of an annular curved surface formed with a continuous curvedsurface enabling to propagate a surface acoustic wave; and

an electro-acoustic transducing element, which excites the surfaceacoustic wave along the surface, which propagates the surface acousticwave along the surface, and which enables to receive the surfaceacoustic wave propagating along the surface,

the device characterized in that the three-dimensional substrate is madeof a Bi₁₂SiO₂₀ crystal, and,

along the surface of the three-dimensional substrate, theelectro-acoustic transducing element propagates the excited surfaceacoustic wave along a line of intersection between a crystal face of theBi₁₂SiO₂₀ crystal and the surface thereof, the line of intersectiondefined as an outermost circumferential line of the surface.

In order to achieve the above described object, another surface acousticwave device according to this invention comprises:

a three-dimensional substrate having a surface, which includes at leasta part of an annular curved surface formed with a continuous curvedsurface enabling to propagate a surface acoustic wave; and

an electro-acoustic transducing element, which excites the surfaceacoustic wave along the surface, which propagates the surface acousticwave along the surface, and which enables to receive the surfaceacoustic wave propagating along the surface,

the device characterized in that the three-dimensional substrate is madeof a Li₂B₄O₇ crystal, and,

along the surface of the three-dimensional substrate, theelectro-acoustic transducing element propagates the excited surfaceacoustic wave along a line of intersection between a crystal face of theLi₂B₄O₇ crystal and the surface thereof, a normal line of the crystalface extending in a direction orthogonal to a C crystal axis of theLi₂B₄O₇ crystal, and the line of intersection defined as an outermostcircumferential line of the surface.

In order to achieve the above described object, a further surfaceacoustic wave device according to this invention comprises:

a three-dimensional substrate having a surface, which includes at leasta part of an annular curved surface formed with a continuous curvedsurface enabling to propagate a surface acoustic wave; and

an electro-acoustic transducing element, which excites the surfaceacoustic wave along the surface, which propagates the surface acousticwave along the surface, and which enables to receive the surfaceacoustic wave propagating along the surface,

the device characterized in that the three-dimensional substrate is madeof a Li₂B₄O₇ crystal, and,

along the surface of the three-dimensional substrate, theelectro-acoustic transducing element propagates the excited surfaceacoustic wave along a line of intersection between a crystal face of theLi₂B₄O₇ crystal and the surface thereof, the normal line of the crystalface extending in a direction inclined between 30° and 40° in anarbitrary direction from a C crystal axis of the Li₂B₄O₇ crystal, andthe line of intersection defined as an outermost circumferential line ofthe surface.

In order to achieve the above described object, a more further surfaceacoustic wave device according to this invention comprises:

a three-dimensional substrate having a surface, which includes at leasta part of an annular curved surface formed with a continuous curvedsurface enabling to propagate a surface acoustic wave; and

an electro-acoustic transducing element, which excites the surfaceacoustic wave along the surface, which propagates the surface acousticwave along the surface, and which enables to receive the surfaceacoustic wave propagating along the surface,

the device characterized in that the three-dimensional substrate is madeof a LiNbO₃ crystal, and,

along the surface of the three-dimensional substrate, theelectro-acoustic transducing element propagates the excited surfaceacoustic wave along at least one of two lines of intersections, one ofwhich is defined between one crystal face of the LiNbO₃ crystal and thesurface thereof, a normal line of the one crystal face being a crystalaxis specified by rotating a +Y axis that is a crystal axis of theLiNbO₃ crystal by 20° in a +Z direction with an X axis being arotational center, and the other of which is defined between the othercrystal face of the LiNbO₃ crystal and the surface thereof, a normalline of the other crystal face being a crystal axis specified byrotating a +Y axis that is a crystal axis of the LiNbO₃ crystal by 26°in a −Z direction with an X axis being a rotational center, and the atleast one of the two lines of intersections defined as an outermostcircumferential line.

In order to achieve the above described object, a more further surfaceacoustic wave device according to this invention comprises:

a three-dimensional substrate having a surface, which includes at leasta part of an annular curved surface formed with a continuous curvedsurface enabling to propagate a surface acoustic wave; and

an electro-acoustic transducing element, which excites the surfaceacoustic wave along the surface, which propagates the surface acousticwave along the surface, and which enables to receive the surfaceacoustic wave propagating along the surface,

the device characterized in that the three-dimensional substrate is madeof a LiTaO₃ crystal, and,

along the surface of the three-dimensional substrate, theelectro-acoustic transducing element propagates the excited surfaceacoustic wave along a line of intersection between a crystal face of theLiTaO₃ crystal and the surface thereof, a normal line of the crystalface being a crystal axis specified by rotating a +Y axis that is acrystal axis of the LitaO₃ crystal by 45° in a −Z direction with an Xaxis being a rotational center, and the line of intersection defined asan outermost circumferential line.

In order to achieve the above described object, a more further surfaceacoustic wave device according to this invention comprises:

a three-dimensional substrate having a surface, which includes at leasta part of an annular curved surface formed with a continuous curvedsurface enabling to propagate a surface acoustic wave; and

an electro-acoustic transducing element, which excites the surfaceacoustic wave along the surface, which propagates the surface acousticwave along the surface, and which enables to receive the surfaceacoustic wave propagating along the surface,

the device characterized in that the three-dimensional substrate is madeof a quartz crystal, and,

along the surface of the three-dimensional substrate, theelectro-acoustic transducing element propagates the excited surfaceacoustic wave along a line of intersection between a crystal face of thequartz crystal and the surface thereof, a normal line of the crystalface being a Y axis that is a crystal axis of the quartz crystal, andthe line of intersection defined as an outermost circumferential line.

In order to achieve the above described object, an environmentaldifference detecting apparatus according to this invention ischaracterized in that:

along the surface of each of the above described surface acoustic wavedevices according to this invention, a plurality of electro-acoustictransducing elements excite surface acoustic waves, propagate thesurface acoustic waves along a plurality of lines of intersection of thesurface of the surface acoustic wave device, and receive the propagatedsurface acoustic waves to output reception signals;

the reception signals outputted from the plurality of electro-acoustictransducing elements are compared with each other; and

an environmental difference in a plurality of portions of a space, withwhich the plurality of portions along the surface propagating theplurality of surface acoustic waves come into contact, is detected.

In the present invention, a pseudo surface acoustic wave or, forexample, a corridor wave, which is excited by an electro-acoustictransducing element immediately beneath a surface of a crystallinematerial forming the three-dimensional substrate, and which ispropagated in the immediately beneath the surface, is referred to as asurface acoustic wave. Further, as is, for example, a boundary acousticwave, even an acoustic wave which propagates along a surface of athree-dimensional substrate on which a different substance adhering thesurface and which is not referred to as a surface acoustic wave ingeneral, is referred to as a surface acoustic wave herein.

Even if any film is formed on a portion of a surface of athree-dimensional substrate along which a surface acoustic wavepropagates, or even if an electro-acoustic transducing element is formedon the surface with any film being sandwiched therebetween, the presenceof such a film is permitted as long as such a film does notsubstantially inhibit a desired propagation of a surface acoustic wave.

Further, in the CLAIMS, DESCRIPTION, and accompanying DRAWINGS of thepresent application, the crystal axes of the LiNbO₂ crystal, the LiTaO₃crystal, and the quartz crystal of the three-dimensional substrate areexpressed by the signs of + and − or X, Y, and Z axes. Such anexpression is a conventionally known expressing method relating to acrystal axis of a piezoelectric crystal.

In the above-described surface acoustic device according to theinvention and in the above-described environmental difference detectingapparatus according to the invention and using the surface acoustic wavedevice according to the invention, the three-dimensional substratehaving the surface capable of propagating the surface acoustic wave isformed of the Bi₁₂SiO₂₀ crystal or the Li₂B₄O₇ crystal. Moreover, alongthe surface of each of the crystals, the surface acoustic wave excitedalong the surface by the electro-acoustic transducing element ispropagated along the line of intersection between the specific crystalface of each of the crystals and the surface thereof, and the line ofintersection is defined as the outermost circumferential line of thesurface. Consequently, it is possible to easily mass-produce the surfaceacoustic wave device at a low cost, and also to make the surfaceacoustic wave device achieve consistently a good surface acoustic wavepropagating performance.

In the above-described surface acoustic device according to theinvention and in the above-described environmental difference detectingapparatus according to the invention and using the surface acoustic wavedevice according to the invention, the three-dimensional substratehaving the surface capable of propagating the surface acoustic wave isformed of the LiNbO₃ crystal, the LiTaO₃ crystal, or the quartz crystal.Moreover, along the surface of each of the crystals, the surfaceacoustic wave excited along the surface by the electro-acoustictransducing element is propagated along the line of intersection betweenthe specific crystal face of each of the crystals and the surfacethereof, and the line of intersection is defined as the outermostcircumferential line of the surface. Consequently, it is possible toeasily mass-produce the surface acoustic wave device at a low cost, andalso to make the surface acoustic wave device achieve consistently agood surface acoustic wave propagating performance.

In order to restrict a generation of noise during a production processof the surface acoustic device or during a use thereof due topyroelectricity with respect to the three-dimensional substrate formedof each of the LiNbO₃ crystal and the LiTaO₃ crystal, conductivity ofthe three-dimensional substrate formed of each of the LiNbO₃ crystal andthe LiTaO₃ crystal can be controlled by applying a surface treatmentthereto.

In the above-described surface acoustic device according to theinvention and in the above-described environmental difference detectingapparatus according to the invention and using the surface acoustic wavedevice according to the invention, each of the LiNbO₃ crystal and theLiTaO₃ crystal, whose composition ratio has been changed and which areapplied with a variety of treatment for controlling a variety ofphysical properties, such as a black lithium niobate and black lithiumtantalite obtained by applying, for example, the above described surfacetreatment, is not excluded.

Further, the present invention does not exclude such a crystal, which iseach of the LiNbO₃ crystal and LiTaO₃ crystal each added with, forexample, magnesium in their crystallization process, or which is each ofthe above-described Bi₁₂SiO₂₀ crystal, Li₂B₄O₇ crystal, LiNbO₃ crystaland LiTaO₃ crystal each changed in composition ratio or added with otherelement in a range of no changing in crystalline system thereof and nolosing piezoelectric characteristics thereof.

The “transmitting and receiving portion” which is described in thepresent invention, for exciting and receiving the surface acoustic wavealong the surface of the three-dimensional substrate, can also beconfigured as two mutually independent portions obtained by dividing thetransmitting and receiving portion in its function into a “transmittingportion” and a “receiving portion”. Where the “transmitting portion” andthe “receiving portion” are configured as mutually independent portions,designs of a drive circuit and a detector circuit for these portions areeasily made. However, in a case where a surface acoustic wave circulatesalong the surface many times, the surface acoustic wave passes throughthe mutually independent “transmitting portion” and “receiving portion”at every circulation. Thus, the propagation efficiency of the surfaceacoustic wave is slightly lowered as compared with a case in which the“transmitting portion” and the “receiving portion” are not configured asmutually independent portions, but no practical problem occurs.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a schematic view of a surface acoustic wave device accordingto a first embodiment of the present invention.

FIG. 2 is a perspective view schematically showing, in a case where awhole three-dimensional substrate of the surface acoustic wave deviceaccording to the first embodiment of the invention is formed of aLi₂B₄O₇ crystal, how to define an outermost circumferential line servingas a reference of a band shaped zone for propagating a surface acousticwave along an outer surface of the three-dimensional substrate, alongone in a group of crystal faces of the Li₂B₄O₇ crystal, and furtherschematically showing a preferred band shaped area for arranging anelectro-acoustic transducing element.

FIG. 3 is a perspective view schematically showing, in the case wherethe whole three-dimensional substrate of the surface acoustic wavedevice according to the first embodiment of the invention is formed ofthe Li₂B₄O₇ crystal, how to define the outermost circumferential lineserving as the reference of the band shaped zone for propagating thesurface acoustic wave along the outer surface of the three-dimensionalsubstrate, along one in another group of crystal faces of the Li₂B₄O₇crystal.

FIG. 4 is a view schematically showing a preferred arrangement of anelectro-acoustic transducing element with respect to the outermostcircumferential line corresponding thereto in the band shapedpropagating surface zone of the three-dimensional substrate of thesurface acoustic wave device according to the first embodiment of theinvention.

FIG. 5 is a view schematically showing a further preferred arrangementof an electro-acoustic transducing element using a ladder shapedelectrode with respect to the outermost circumferential linecorresponding thereto in the band shaped propagating surface zone of thethree-dimensional substrate of the surface acoustic wave deviceaccording to the first embodiment of the invention.

FIG. 6 is a perspective view schematically showing a surface acousticwave device according to a second embodiment of the present invention.

FIG. 7 is a perspective view schematically showing a surface acousticwave device according to a third embodiment of the present invention.

FIG. 8 is a perspective view schematically showing a surface acousticwave device according to a fourth embodiment of the present invention.

FIG. 9 is a partial cross sectional view schematically showing that anelectro-acoustic transducing element is formed on a base for thethree-dimensional substrate of the surface acoustic wave device shown inFIG. 8 so as to be arranged to face a band shaped propagating surfacezone along the outer surface of the three-dimensional substrate with apredetermined gap therebetween.

FIG. 10 is a perspective view schematically showing a surface acousticwave device according to a fifth embodiment of the present invention.

FIG. 11 is a schematic view of a surface acoustic wave device accordingto a sixth embodiment of the present invention.

FIG. 12 is a perspective view schematically showing, in a case where awhole three-dimensional substrate of the surface acoustic wave deviceaccording to the sixth embodiment of the invention is formed of a LiNbO₃crystal, how to define an outermost circumferential line serving as areference of a band shaped zone for propagating a surface acoustic wavealong an outer surface of the three-dimensional substrate, along one ofthree crystal faces of the LiNbO₃ crystal.

FIG. 13 is a schematic view in which the three-dimensional substrate ofFIG. 12 is seen from a +Z direction side toward a −Z direction side inorder to show three outermost circumferential lines serving asreferences for three band shaped propagating surface zones set along theouter surface of the three-dimensional substrate as shown in FIG. 12.

FIG. 14 is a perspective view schematically showing, in the case wherethe whole three-dimensional substrate of the surface acoustic wavedevice according to the sixth embodiment of the invention is formed ofthe LiNbO₃ crystal, how to define an outermost circumferential lineserving as a reference of a band shaped zone for propagating a surfaceacoustic wave along an outer surface of the three-dimensional substrate,along one of other three crystal faces of the LiNbO₃ crystal.

FIG. 15 is a schematic view in which the three-dimensional substrate ofFIG. 14 is seen from a +Z direction side toward a −Z direction side inorder to show three outermost circumferential lines serving asreferences for other three band shaped propagating surface zones setalong the outer surface of the three-dimensional substrate as shown inFIG. 14.

FIG. 16 is a view schematically showing a preferred arrangement of anelectro-acoustic transducing element with respect to the outermostcircumferential line corresponding thereto in the band shapedpropagating surface zone of the three-dimensional substrate of thesurface acoustic wave device according to the sixth embodiment of theinvention.

FIG. 17 is a view schematically showing a further preferred arrangementof an electro-acoustic transducing element using a ladder shapedelectrode with respect to the outermost circumferential linecorresponding thereto in the band shaped propagating surface zone of thethree-dimensional substrate of the surface acoustic wave deviceaccording to the sixth embodiment of the invention.

FIG. 18 is a perspective view schematically showing, in a case where awhole three-dimensional substrate of the surface acoustic wave deviceaccording to a first modification of the sixth embodiment of theinvention is formed of a LiTaO₃ crystal, how to define an outermostcircumferential line serving as a reference of a band shaped zone forpropagating a surface acoustic wave along an outer surface of thethree-dimensional substrate, along one of three crystal faces of theLiTaO₃ crystal.

FIG. 19 is a schematic view in which the three-dimensional substrate ofFIG. 18 is seen from a +Z direction side toward a −Z direction side inorder to show three outermost circumferential lines serving asreferences for three band shaped propagating surface zones set along theouter surface of the three-dimensional substrate as shown in FIG. 18.

FIG. 20 is a perspective view schematically showing, in a case where awhole three-dimensional substrate of the surface acoustic wave deviceaccording to a second modification of the sixth embodiment of theinvention is formed of a quartz crystal, how to define an outermostcircumferential line serving as a reference of a band shaped zone forpropagating a surface acoustic wave along an outer surface of thethree-dimensional substrate, along one of three crystal faces of thequartz crystal.

FIG. 21 is a schematic view in which the three-dimensional substrate ofFIG. 20 is seen from a +Z direction side toward a −Z direction side inorder to show three outermost circumferential lines serving asreferences for three band shaped propagating surface zones set along theouter surface of the three-dimensional substrate as shown in FIG. 20.

FIG. 22 is a perspective view schematically showing a surface acousticwave device according to a seventh embodiment of the present invention.

FIG. 23 is a perspective view schematically showing a surface acousticwave device according to a modification of the seventh embodiment shownin FIG. 22.

FIG. 24 is a perspective view schematically showing a surface acousticwave device according to an eighth embodiment of the present invention.

FIG. 25 is a perspective view schematically showing a surface acousticwave device according to a ninth embodiment of the present invention.

FIG. 26 is a partial cross sectional view schematically showing that anelectro-acoustic transducing element is formed on a base for thethree-dimensional substrate of the surface acoustic wave device shown inFIG. 25 so as to be arranged to face a band shaped propagating surfacezone along the outer surface of the three-dimensional substrate with apredetermined gap therebetween.

FIG. 27 is a perspective view schematically showing a surface acousticwave device according to a tenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

Hereinafter, a first embodiment of a surface acoustic wave deviceaccording to the present invention will be described in detail withreference to FIGS. 1 to 3 in the accompanying drawings.

FIG. 1 shows an appearance of a surface acoustic wave device 10according to the first embodiment. The surface acoustic wave device 10comprises: a three-dimensional substrate 12 having a surface, whichincludes a band shaped propagating surface zone 12 a formed of at leasta part of a continuous annular curved surface enabling to propagate asurface acoustic wave; and an electro-acoustic transducing element 14,which excites the surface acoustic wave along the band shapedpropagating surface zone 12 a, which propagates the surface acousticwave along the band shaped propagating surface zone 12 a, and whichenables to receive the surface acoustic wave propagating along the bandshaped propagating surface zone 12 a.

Here, the band shaped propagating surface zone 12 a is drawn such that adimension in its widthwise direction W is uniform at any points in adirection in which the band shaped propagating surface zone 12 a iscontinuous in the annular shape, in order to simplify the drawing ofFIG. 1. However, actually, while the surface acoustic wave propagates inthe direction in which the band shaped propagating surface zone 12 a iscontinuous in the annular shape along the surface of thethree-dimensional substrate 12, the dimension of the surface acousticwave in the widthwise direction W may be uniform as shown in FIG. 1 ormay repeatedly diverge and converge.

In any case, it is practically desired that the surface acoustic wavepropagates along the band shaped propagating surface zone 12 a for adesired distance from the electro-acoustic transducing element 14 or perone circulation, while keeping at least 80% or more of energy thereof.

In this embodiment, whole of the three-dimensional substrate 12 isformed of a Li₂B₄O₇ crystal in a spherical shape. Therefore, in thisembodiment, the band shaped propagating surface zone 12 a is continuousin the annular shape along the spherically shaped surface of thethree-dimensional substrate 12. The band shaped propagating surface zone12 a is continuous along an outermost circumferential line 12 b of thethree-dimensional substrate 12, and preferably, the outermostcircumferential line 12 b is included in the range of the band shapedpropagating surface zone 12 a.

On the outer surface of the three-dimensional substrate 12, theoutermost circumferential line 12 b, as shown in FIG. 2, coincides witha line of intersection between one crystal face of the Li₂B₄O₇ crystaland the outer surface of the three-dimensional substrate 12, a normalline of the crystal face extending in a direction CA inclined between30° and 40° in an arbitrary direction from a C crystal axis of theLi₂B₄O₇ crystal (wherein the above described arbitrary direction is anarbitrary angle direction in a whole circumference of 360° around the Ccrystal axis). That is, the outermost circumferential line 12 b alongwhich the band shaped propagating surface zone 12 a extends along onecrystal face of the Li₂B₄O₇ crystal on the outer surface of thethree-dimensional substrate 12. While the surface acoustic wavepropagates along the above described crystal face on the outer surfaceof the three-dimensional substrate 12, a large energy diffusion of thesurface acoustic wave, which is generated in a case where the surfaceacoustic wave propagates along the outer surface to cross the abovecrystal face, will not occur. Thus, the surface acoustic wave canpropagate most efficiently along the outer surface of thethree-dimensional substrate 12.

On the outer surface of the three-dimensional substrate 12 according tothe first embodiment, whole of which is formed of the Li₂B₄O₇ crystal,the outermost circumferential line 12 b, along which the band shapedpropagating surface zone 12 a is continuous, can be specified asfollows.

That is, on the outer surface of the three-dimensional substrate 12, theoutermost circumferential line 12 b, as shown in FIG. 3, is aligned witha line of intersection between other crystal face of the Li₂B₄O₇ crystaland the outer surface of the three-dimensional substrate 12, a normalline of the other crystal face extending in a direction CB, which isorthogonal to the C crystal axis of the Li₂B₄O₇ crystal. This means thatthe outermost circumferential line 12 b on the outer surface of thethree-dimensional substrate 12, along which the band shaped propagatingsurface zone 12 a extends along a crystal face specified independentlyof the crystal face, the normal line of which extends in the directionCA inclined between 30° and 40° in the arbitrary direction from the Ccrystal axis of the Li₂B₄O₇ crystal (wherein the above describedarbitrary direction is the arbitrary angle direction in the wholecircumference of 360° around the C crystal axis). While the surfaceacoustic wave propagates along the above described other specifiedcrystal face on the outer surface of the three-dimensional substrate 12,a large energy diffusion of the surface acoustic wave will not occur ina direction orthogonal to the above described other specified crystalface, as in the case of the crystal face described with reference toFIG. 2. Thus, the surface acoustic wave can propagate most efficientlyalong the outer surface of the three-dimensional substrate 12.

In addition, it is possible to visually estimate an actual width of thesurface acoustic wave, which propagates along the surface of thethree-dimensional substrate 12, in a direction orthogonal to itspropagating direction along the surface, because, for example, afterdepositing water droplets on the surface, the surface acoustic wave doesnot propagate along a portion of the surface on which water droplets aredeposited.

In general, in a case where a surface acoustic wave having a highfrequency is excited by using a ladder shaped electrode as anelectro-acoustic transducing element, an effective width of the laddershaped electrode (that is, a dimension of a portion of the ladder shapedelectrode, at that portion the ladder shaped electrode enables to excitea surface acoustic wave along the surface of the three-dimensionalsubstrate and to propagate the excited wave in a desired direction andto receive the surface acoustic wave propagating along the surface, in adirection orthogonal to the desired direction along the surface) isreduced. However, it is found that a surface acoustic wave exciting andreceiving efficiency of the effective width of the ladder shapedelectrode is extremely lowered where the effective width is greater than1.5 times of a radius of curvature of a band shaped propagating surfacezone (designated by reference numeral 12 a in FIG. 1) on the outersurface in a direction, which is the above desired direction, orthogonalto an outermost circumferential line (designated by reference numeral 12b in FIG. 1).

Portions of the outer surface of the three-dimensional substrate 12,which are other than the propagating surface zone 12 a along which thesurface acoustic wave excited by the electro-acoustic transducingelement 14 propagates, are supported on a base 18 by supporting arms 16.In order to have no effect on the surface acoustic wave propagatingalong the propagating surface zone 12 a, nothing but theelectro-acoustic transducing element 14 is brought into contact with thepropagating surface zone 12 a. Therefore, in the present embodiment, anelectro-acoustic transducing element control unit 20, which is formaking the electro-acoustic transducing element 14 to excite the surfaceacoustic wave along the propagating surface zone 12 a and for receivinga signal from the electro-acoustic transducing element 14 when theelectro-acoustic transducing element 14 receives the surface acousticwave propagating along the propagating surface zone 12 a, is connectedto the electro-acoustic transducing element 14 by lead wires extendingfrom the electro-acoustic transducing element 14 on the portions of theouter surface of the three-dimensional substrate 12 other than thepropagating surface zone 12 a. The electro-acoustic transducing elementcontrol unit 20 comprises, for example, an impedance matching circuit 20a, a circulator 20 b, an oscillator 20 c including a high frequencypower supply, an amplifier 20 d, and a digital oscilloscope 20 e, etc.as shown in FIG. 1. A high frequency radio wave receiving antenna canalso be used instead of the oscillator 20 c.

As shown in FIG. 4, it is preferable that the electro-acoustictransducing element 14 is configured so that an orientation MD, in whicha flow density of energy of a surface acoustic wave excited along thepropagating surface zone 12 a becomes maximum, is within 20° withrespect to the outermost circumferential line 12 b. This angle is morepreferably within 10°, and further preferably within 5°. This meansthat, as long as the surface acoustic wave excited along the propagatingsurface zone 12 a by the electro-surface transducing element 14 cancirculate at a small attenuation rate such that, for example, 80% ormore of energy can be maintained every circulation along the outermostcircumferential line 12 b on the outer surface of the three-dimensionalsubstrate 12, the surface acoustic wave may tends to be diffused fromthe outermost circumferential line 12 b more than a width of the surfaceacoustic wave immediately after it is excited, while the surfaceacoustic wave propagates, but it is preferable that the surface acousticwave is excited by the electro-surface transducing element 14 such thatthe orientation MD is within the above described angles.

A phrase “along the outermost circumferential line” described withrespect to the present invention means a case in which, when the surfaceacoustic wave circulates or propagates along a propagation passage, adirection, in which the flow density of energy of the surface acousticwave becomes maximum, is preferably within 20°, more preferably within10°, and further preferably within 5° with respect to the outermostcircumferential line.

In this embodiment, the electro-acoustic transducing element 14 isdirectly formed on the outer surface of the three-dimensional substrate12 within the propagating surface zone 12 a. In this embodiment, theelectro-acoustic transducing element 14 is a ladder shaped electrode 22such as, for example, a comb shaped electrode, and can be directlyformed on the outer surface with a variety of publicly known processessuch as, for example, vapor deposition, printing, sputtering, andsol-gel techniques.

In the case where the electro-acoustic transducing element 14 is formedof the ladder shaped electrode 22, it is preferable that, as well shownin FIG. 5, the ladder shaped electrode 22 is configured so that a lineextending along the outer surface of the three-dimensional substrate 12and being orthogonal to a transmitting and receiving portion (a portionof the above described effective width) of the ladder shaped electrode22 capable of exciting a surface acoustic wave along the propagatingsurface zone 12 a and receiving the surface acoustic wave propagatingalong the propagating surface zone 12 a, is included in a range equal toor smaller than 10° with respect to the outermost circumferential line12 b, along which the propagating surface zone 12 a extends. In moredetail, this means that it is preferable that an orthogonal line OL,which extends along the outer surface of the propagating surface zone 12a and which is orthogonal to the transmitting and receiving portion ateach terminal (line element) 22 a in the pattern of the ladder shapedelectrode 22 [in the case of the ladder shaped electrode 22, thetransmitting and receiving portion at each terminal (line element) 22 ain the pattern of the ladder shaped electrode 22, overlapping each otherin a direction along the outermost circumferential line 12 b], is in arange equal to or smaller than 10° with respect to the outermostcircumferential line 12 b.

The reason is identical to the reason why it is preferable that theelectro-acoustic transducing element 14 is configured so that theorientation MD, in which the flow density of energy of the surfaceacoustic wave excited along the propagating surface zone 12 a becomesmaximum, is within 20° with respect to the outermost circumferentialline 12 b, as described previously with reference to FIG. 4.

Further, it is preferable that an arrangement pitch P of the pluralityof terminals 22 a (see FIG. 5) in the pattern of the ladder shapedelectrode 22 in a direction along the outermost circumferential line 12b is equal to or smaller than 1/10 of the radius of curvature of theoutermost circumferential line 12 b. The arrangement pitch P isequivalent to one wavelength (i.e., vibration cycle) of the surfaceacoustic wave excited by the ladder shaped electrode 22.

When the wavelength of the surface acoustic wave (i.e., the arrangementpitch P of the plurality of terminals 22 a in the pattern of the laddershaped electrode 22) is greater than 1/10 of the radius of curvature ofthe outermost circumferential line 12 b included in the propagatingsurface zone 12 a along which the surface acoustic wave propagates (inthe case where the propagating surface zone 12 a is a part of thespherical surface as in this embodiment, the radius of curvature is aradius of the spherical surface), a function of a geometrical feature ofthe curved propagating surface zone 12 a to restrict diffusion of thesurface acoustic wave propagating along the propagating surface zone 12a becomes weak. Therefore, in order to propagate a surface acoustic wavehaving a comparatively long wavelength along the propagating surfacezone 12 a on the surface of the three-dimensional substrate 12 for adesired distance, the radius of curvature of the outermostcircumferential line 12 b included in the propagation surface zone 12 amust be preset so as to meet the above-described relationship with theabove wavelength.

Consequently, it is preferable that the arrangement pitch is defined asdescribed above to efficiently propagate a surface acoustic wave alongthe propagating surface zone 12 b.

Further, in the case where the three-dimensional substrate 12 is formedof the Li₂B₄O₇ crystal as described above, it is found to be preferablethat the transmitting and receiving portion of the electro-acoustictransducing element 14, which is capable of exciting a surface acousticwave along the outer surface of the three-dimensional substrate 12,propagating the surface acoustic wave along the surface, and receivingthe surface acoustic wave propagating along the outer surface, isarranged so as to include a part of the line of intersection (outermostcircumferential line 12 b) on the outer surface of the three-dimensionalsubstrate 12. With such an arrangement, an efficiency of thetransmitting and receiving portion of the electro-acoustic transducingelement 14 to excite and receive the surface acoustic wave can beimproved more remarkably.

In addition to such an arrangement, in the case where thethree-dimensional substrate 12 is formed of the Li₂B₄O₇ crystal asdescribed above, and the outermost circumferential line 12 b isspecified as shown in FIG. 2, it is found to be further preferable that,in order to improve the above-described efficiency of the transmittingand receiving portion of the electro-acoustic transducing element 14more remarkably, the transmitting and receiving portion of theelectro-acoustic transducing element 14 is arranged in a band shapedarea AA, which is defined between 75° and 105° in an arbitrary directionfrom the C axis described above, on the outer surface of thethree-dimensional substrate 12.

When the spherically shaped three-dimensional substrate 12 is presumedas the earth, the C axis is equivalent to the earth's axis of the earth,and the outermost circumferential line 12 b specified as shown in FIG. 3is equivalent to the longitude line on the earth. In addition, the bandshaped area AA specified as shown in FIG. 2 is equivalent to a bandshaped portion that is sandwiched between latitude 15° north andlatitude 15° south and that continuously extends in an annular shapealong the equator.

In FIG. 2, only a portion of the band shaped area AA which can be seenon the outer surface of the three-dimensional substrate 12 is shown inorder to avoid complication of the figure. However, in actuality, theband shaped area AA continuously extends even in a portion of the outersurface of the three-dimensional substrate 12, which cannot be seen onthe outer surface of the three-dimensional substrate 12, and forms anannular shape.

First Modification of First Embodiment

Now, a first modification of the first embodiment of the surfaceacoustic wave device according to the present invention will bedescribed in detail.

In a surface acoustic wave device of this modification, thethree-dimensional substrate 12, which is formed of the Li₂B₄O₇ in thefirst embodiment, is formed of a Bi₁₂SiO₂₀ crystal in a spherical shape.Concurrently, a method for specifying the outermost circumferential line12 b on the outer surface of the three-dimensional substrate 12 is alsodifferent from that in the case of the three-dimensional substrate 12formed of the Li₂B₄O₇ in the first embodiment described previously.However, structural elements other than those described above areidentical to those of the surface acoustic device of the firstembodiment described previously.

In the surface acoustic wave device of this modification, the outermostcircumferential line 12 b on the outer surface of the three-dimensionalsubstrate 12 formed of the Bi₁₂SiO₂₀ crystal is aligned with a line ofintersection between a crystal face (111) of the Bi₁₂SiO₂₀ crystal andthe outer surface of the three-dimensional substrate 12. Also, while asurface acoustic wave propagates along such one crystal face along theouter surface of the three-dimensional substrate 12, significantdiffusion of energy of the surface acoustic wave does not occur in adirection intersecting with the above-described crystal face, as is thecase with the crystal face of the first embodiment described previously.Thus, it is possible to most efficiently propagate the surface acousticwave along the outer surface of the three-dimensional substrate 12.

Second Embodiment

Now, a second embodiment of the surface acoustic wave device accordingto the present invention will be described in detail with reference toFIG. 6.

In a surface acoustic wave device 30 of this embodiment,electro-acoustic transducing elements 14 are formed as described abovealong portions on an arbitrary plurality of propagating surface zones 12a that can be specified as described above on the outer surface of thethree-dimensional substrate 12 of the surface acoustic wave device 10according to the above-described first embodiment or the modificationthereof, that portions on the arbitrary plurality of propagating surfacezones 12 a not intersecting with other propagating surface zone 12 a.And, each of the electro-acoustic transducing elements 14 is connectedto the electro-acoustic element control unit 20 described above.

In FIG. 6, only portions of the band shaped zones 12 a which can be seenon the outer surface of the three-dimensional substrate 12 are shown inorder to avoid complication of the figure. However, in actuality, theband shaped zones 12 a continuously extend even in a portion of theouter surface of the three-dimensional substrate 12, which cannot beseen on the outer surface of the three-dimensional substrate 12, andeach band shaped zone 12 a forms an annular shape.

Herein, in the case where the three-dimensional substrate 12 is formedof the Li₂B₄O₇ crystal as described above, it is preferable thattransmitting and receiving portion of the electro-acoustic transducingelement 14, which is capable of exciting a surface acoustic wave alongthe outer surface of the three-dimensional substrate 12 and propagatingthe surface acoustic wave along the outer surface and receiving thesurface acoustic wave propagating along the outer surface, is arrangedso as to include a part of the line of intersection (outermostcircumferential line 12 b) on the outer surface of the three-dimensionalsubstrate 12. Such an arrangement of the transmitting and receivingportion of the electro-acoustic transducing element 14 can improve thesurface acoustic more remarkably.

In addition to such an arrangement, in the case where thethree-dimensional substrate 12 is formed of the Li₂B₄O₇ crystal asdescribed above and the outermost circumferential line 12 b is specifiedas shown in FIG. 2, it is further preferable that the transmitting andreceiving portion of the electro-acoustic transducing element 14 isarranged in the band shaped area AA between 75° and 105° from the C axisin the arbitrary direction as described above in order to improve theabove-described efficiency of the transmitting and receiving portion ofthe electro-acoustic transducing element 14 more remarkably.

Further, in this embodiment, a support member 32 for supporting thethree-dimensional substrate 12 on any base (not shown) is fixed at aposition on the outer surface of the three-dimensional substrate 12excluding a plurality of propagating surface zones 12 a and the bandshaped area AA, in which the electro-acoustic transducing elements 14are formed.

The surface acoustic wave device 30 according to the second embodimentand configured as described above is more excellent when it is used asan environmental difference detecting apparatus, as compared with thesurface acoustic wave device 10 according to each of the firstembodiment and the modification thereof. The reason is as follows.

In the case that one electro-acoustic transducing element 14 and oneelectro-acoustic transducing element control unit 20 connected theretoare used as in the surface acoustic wave device 10 described above, whenany physical change (for example, expansion or contraction of thethree-dimensional substrate 12 due to a temperature change in anexternal environment) occurs in the surface acoustic wave device 10 dueto an effect of a change in the external environment described above, aslight change occurs in a propagation speed of the surface acoustic wavepropagating along the propagating surface zone 12 a or in a propagationtime required for one circulation.

Therefore, in order to detect more precisely a change of a fluid (gas orliquid) filled in a space, with which the propagating surface zone 12 acomes into contact (i.e., change in external environment, with which thepropagating surface zone 12 a comes into contact), a physical change ofthe surface acoustic wave device 10 due to an effect of the change inthe external environment described above must be considered.

The surface acoustic wave device 30 of the second embodiment describedwith reference to FIG. 6 is configured so that at least one of theplurality of propagating surface zones 12 a, along which theelectro-acoustic transducing elements 14 are formed, on the outersurface of the three-dimensional substrate 12 is isolated from anexternal environment in which a change is to be detected, and that atleast another of the plurality of propagating surface zones 12 a, alongwhich the electro-acoustic transducing elements 14 are formed, isbrought into contact with the external environment.

With such a configuration, a signal, which is received from theelectro-acoustic transducing element 14 along the propagating surfacezone 12 a isolated from the external environment by the above describedelectro-acoustic transducing element control unit 20 corresponding tothe transducing element along the isolated propagating surface zone,indicates a physical change of the surface acoustic wave device 10 dueto the change in the external environment. In addition, a signal, whichis received from the electro-acoustic transducing element 14 alonganother propagating surface zone 12 a being in contact with the externalenvironment by the above described electro-acoustic transducing elementcontrol unit 20 corresponding to the transducing element along thecontacted propagating surface zone, indicates a change in externalenvironment, together with the physical change of the surface acousticwave device 10 due to the change in external environment.

Therefore, by subtracting the signal, which is received from theelectro-acoustic transducing element 14 along the propagating surfacezone 12 a isolated from the external environment by the electro-acoustictransducing element control unit 20 corresponding to theelectro-acoustic transducing element along the isolated propagatingsurface zone, from the signal, which is received from theelectro-acoustic transducing element 14 along another propagatingsurface zone 12 a being in contact with the external environment by theelectro-acoustic transducing element control unit 20 corresponding tothe electro-acoustic transducing element along the contacted propagatingsurface zone, it possible to detect only a pure change in the externalenvironment.

Third Embodiment

Now, a third embodiment of the surface acoustic wave device according tothe present invention will be described in detail with reference to FIG.7.

In a surface acoustic wave device 40 according to the third embodiment,the three-dimensional substrate 12 has a recessed portion or hollowportion, and the recessed portion or an inner surface 12 c of the hollowportion includes the propagating surface zone 12 a, along which asurface acoustic wave can propagate and which is a curved surfacecontinuous in an annular shape. FIG. 7 shows the three-dimensionalsubstrate 12 having a through hole that is a kind of the hollow portion.

The whole of three-dimensional substrate 12 is formed of a Li₂B₄O₇crystal or Bi₁₂SiO₂₀ crystal as in the three-dimensional substrate 12according to the above-described first embodiment or its modification.In addition, at least one outermost circumferential line 12 b, whichbecomes a reference along which the band shaped propagating surface zone12 a extends, is specified on the inner surface of the three-dimensionalsubstrate 12 of the surface acoustic wave device 40 according to thethird embodiment, along a line of intersection between at least one of aplurality of crystal faces specific to the crystal forming thethree-dimensional substrate 12 and the inner surface thereof, in thesame manner as in the case where the outermost circumferential line 12 bis specified on the outer surface of the three-dimensional substrate 12according to the above-described first embodiment and its modification,the outermost circumferential line 12 b serving as the reference for thepropagating surface zone 12 a along the line of intersection between atleast one of the plurality of crystal faces specific to the crystalforming the three-dimensional substrate 12 and the outer surfacethereof. And, the propagating surface zone 12 a is specified so as toextend continuously along the outermost circumferential line 12 b on theinner surface. A method for specifying the propagating surface zone 12 aalong the inner surface of the three-dimensional substrate 12 accordingto the present embodiment is identical to that for specifying thepropagating surface zone 12 a along the outer surface of thethree-dimensional substrate 12 according to the above-described firstembodiment and its modification. Therefore, the outermostcircumferential line 12 b is preferably included in the range of thepropagating surface zone 12 a along the inner surface.

And, in the propagating surface zone 12 a along the inner surface of thethree-dimensional substrate 12 of this embodiment, the electro-acoustictransducing element 14 is formed so as to propagate the surface acousticwave along the outermost circumferential line 12 b in the range of thepropagating surface zone 12 a without significantly attenuating it, andthe above described electro-acoustic transducing element control unit 20is connected to the electro-acoustic transducing element 14.

Also, in this embodiment, a portion of the inner surface other than thepropagating surface zone 12 a may be formed in an arbitrary shape aslong as the propagating surface zone 12 a is specified in accordancewith the above described predetermined method.

In this embodiment, the acoustic surface wave, which is excited alongthe propagating surface zone 12 a by the electro-acoustic transducingelement 14 and which propagates along the propagating surface zone 12 awhile keeping its energy of, for example, 80% or more per onecirculation without significant attenuation, changes in response to avariety of changes in a fluid (gas or liquid) passing through theinternal space of a through hole that is an environment, with which thepropagating surface zone 12 a along the inner surface of thethree-dimensional substrate 12 comes into contact. And, the surfaceacoustic wave device 40 of the present embodiment can detect a change inthe environment, i.e., a difference in the environment, by receiving thechange in the signal, which is generated from the electro-acoustictransducing element 14, in the electro-acoustic transducing elementcontrol unit 20.

Further, in this embodiment, as in the surface acoustic wave device 30of the second embodiment described above with reference to FIG. 6, aplurality of electro-acoustic transducing elements 14, each of which isconnected to the electro-acoustic transducing element control unit 20,can be formed along a plurality of propagating surface zones 12 a alonga plurality of outermost circumferential lines 12 b aligned with aplurality of lines of intersection between a plurality of crystal faces,which are specific to the crystal forming the three-dimensionalsubstrate 12, and the inner surface, with excluding intersectingportions, at which the plurality of propagating surface zones 12 aintersect with each other. With this configuration, as in the surfaceacoustic wave device 30 of the second embodiment described above withreference to FIG. 6, the surface acoustic device can be used as anenvironmental difference detecting apparatus, which is capable ofdetecting an environmental difference more precisely.

Furthermore, in the present embodiment, as in the surface acoustic wavedevice 30 of the second embodiment described above with reference toFIG. 6, it is preferable that, in the case where the three-dimensionalsubstrate 12 is formed of the Li₂B₄O₇ crystal as described above, thetransmitting and receiving portion of the electro-acoustic transducingelement 14, which is capable to excite the surface acoustic wave alongthe inner surface of the three-dimensional substrate 12 and to propagatethe surface acoustic wave along the inner surface and to receive thesurface acoustic wave propagating along the inner surface, includes apart of the line of intersection (outermost circumferential line 12 b)on the inner surface of the three-dimensional substrate 12. With such anarrangement of the transmitting and receiving portion of theelectro-acoustic transducing element 14, it is possible to improveefficiency of the transmitting and receiving portion of theelectro-acoustic transducing element 14 for exciting and receiving thesurface acoustic wave.

In addition to such an arrangement, in the case where thethree-dimensional substrate 12 is formed of the Li₂B₄O₇ crystal asdescribed above and the outermost circumferential line 12 b is specifiedas shown in FIG. 2, it is more preferable that the transmitting andreceiving portion of the electro-acoustic transducing element 14 isarranged in the band shaped area AA indicating between 75° and 105° inthe arbitrary direction from the above described C axis in order toimprove the above-described efficiency of the transmitting and receivingportion of the electro-acoustic transducing element 14 more remarkably.

Fourth Embodiment

Now, a fourth embodiment of the surface acoustic wave device accordingto the present invention will be described in detail with reference toFIGS. 8 and 9.

A surface acoustic wave device 50 according to the fourth embodimentcomprises the spherically shaped three-dimensional substrate 12, thewhole of which is formed of the Li₂B₄O₇ crystal or Bi₁₂SiO₂₀ crystal, asin the three-dimensional substrate 12 according to the above-describedfirst embodiment and its modification. Along the outer surface of thethree-dimensional substrate 12, a propagating surface zone 12 a isspecified so that the propagating surface zone 12 a is continuous in anannular shape along the outermost circumferential line 12 b, which is atleast one of the plurality of lines of intersection between theplurality of crystal faces of the material for the three-dimensionalsubstrate 12 and the outer surface thereof. The propagating surface zone12 a along the outer surface of the three-dimensional substrate 12 ofthe surface acoustic wave device 50 according to the present embodimentalso preferably includes the outermost circumferential line 12 b in therange of the propagating surface zone 12 a, as in the propagatingsurface zone 12 a along the outer surface of the three-dimensionalsubstrate 12 according to the above-described first embodiment and itsmodification.

The surface acoustic wave device 50 of this embodiment is different fromthe surface acoustic wave device 10 according to the first embodiment orits modification in that the electro-acoustic transducing element 14,which is capable of exciting the surface acoustic wave along thepropagating surface zone 12 a along the outer surface of thethree-dimensional substrate 12 and propagating the excited surfaceacoustic wave along the outermost circumferential line 12 b in the rangeof the propagating surface zone 12 a, is not directly formed on theouter surface of the three-dimensional substrate 12 within thepropagating surface zone 12 a.

In this embodiment, a base 52 for supporting a portion of the outersurface of the three-dimensional substrate 12 other than the propagatingsurface zone 12 a has a propagating surface zone facing region 52 afacing the propagating surface zone 12 a with a predetermined gap Stherebetween, and the electro-acoustic transducing element 14 is formedon the propagating surface zone facing region 52 a of the base 52. Thedimensions of the electro-acoustic transducing element 14 and thearrangement thereof with respect to the propagating surface zone 12 aare identical to those in the case where the electro-acoustictransducing element 14 is directly formed on the outer surface of thethree-dimensional substrate 12 within the propagating surface zone 12 ain the surface acoustic wave device 10 according to the first embodimentor its modification.

In a case where the electro-acoustic transducing element 14 is theladder shaped electrode 22 such as a comb shaped electrode, it ispreferable that the predetermined gap S is equal to or smaller than ¼ ofthe arrangement pitch P (refer to FIG. 5) of the plurality of lineelements (terminals) in the pattern of the ladder shaped electrode 22.When the predetermined gap S is greater than ¼ of the arrangement pitchP (refer to FIG. 5), it becomes difficult for the electro-acoustictransducing element 14 to always reliably excite a desired surfaceacoustic wave along the propagating surface zone 12 a along the outersurface of the three-dimensional substrate 12.

The surface acoustic wave device 50 according to the fourth embodimentcan be used in the same manner as that in the three-dimensionalsubstrate 12 according to the above-described first embodiment and itsmodification. Where the electro-acoustic transducing element 14 isdirectly formed on the outer surface of the three-dimensional substrate12 within the propagating surface zone 12 a, the directly formedelectro-acoustic transducing element 14 within the propagating surfacezone 12 a may very slightly affect the surface acoustic wave, which isexcited and propagated along the propagating surface zone 12 a. But, inthe case where the electro-acoustic transducing element 14 faces thepropagating surface zone 12 a along the outer surface of thethree-dimensional substrate 12 with the predetermined gap Stherebetween, the above described adverse effect, which may be caused bythe electro-acoustic transducing element 14 directly formed on the outersurface of the three-dimensional substrate 12 within the propagatingsurface zone 12 a, can be eliminated. Consequently, in this embodiment,a change in the surface acoustic wave propagating along the propagatingsurface zone 12 a can be sensed more precisely.

Further, in this embodiment, as in the surface acoustic wave device 30of the second embodiment described above with reference to FIG. 6,propagating surface zone facing regions 52 a of a plurality of bases 52can be faced to a plurality of propagating surface zones 12 a along aplurality of outermost circumferential lines 12 b aligned with aplurality of lines of intersection between a plurality of crystal faces,which are specific to the crystal forming the three-dimensionalsubstrate 12, and the outer surface thereof, excluding intersectingportions, at which the propagating surface zones 12 a intersect witheach other. And also, in this case, as in the surface acoustic wavedevice 30 of the second embodiment described above with reference toFIG. 6, the surface acoustic device can be used as an environmentaldifference detecting apparatus capable of more precisely detecting anenvironmental difference.

Furthermore, in this embodiment, as in the surface acoustic wave device30 of the second embodiment described above with reference to FIG. 6,where the three-dimensional substrate 12 is formed of the Li₂B₄O₇crystal as described above, it is preferable that the transmitting andreceiving portion of the electro-acoustic transducing element 14, whichis capable of exciting the surface acoustic wave along the outer surfaceof the three-dimensional substrate 12 and propagating the surfaceacoustic wave along the outer surface and receiving the surface acousticwave propagating along the outer surface, is arranged so as to include apart of the line of intersection (outermost circumferential line 12 b)along the outer surface of the three-dimensional substrate 12. With suchan arrangement, it is possible to improve the efficiency of thetransmitting and receiving portion of the electro-acoustic transducingelement 14 for exciting and receiving the surface acoustic wave.

In addition to such an arrangement, in the case where thethree-dimensional substrate 12 is formed of the Li₂B₄O₇ crystal asdescribed above and the outermost circumferential line 12 b is specifiedas shown in FIG. 2, it is more preferable that the transmitting andreceiving portion of the electro-acoustic transducing element 14 isarranged along the outer surface of the three-dimensional substrate 12in the band shaped area AA indicating between 75° and 105° in thearbitrary direction from the above described C axis as shown in FIG. 2,in order to improve the above described efficiency of the transmittingand receiving portion of the electro-acoustic transducing element 14more remarkably.

Fifth Embodiment

Now, a fifth embodiment of the surface acoustic wave device according tothe present invention will be described in detail with reference to FIG.10.

A surface acoustic wave device 60 according to the fifth embodimentcomprises a three-dimensional substrate 12′ having a semisphericalshape, and an outer surface of the three-dimensional substrate 12′includes a band shaped propagating surface zone 12′a made of at least apart of an annular continuous curved surface along which a surfaceacoustic wave can propagate.

The whole of the semi-spherically shaped three-dimensional substrate 12′is formed of a Li₂B₄O₇ crystal or Bi₁₂SiO₂₀ crystal, as in thethree-dimensional substrate 12 according to the above-described firstembodiment and its modification. And, at least one outermostcircumferential line 12′b, which serves as a reference for extending thepropagation surface zone 12′a continuously, is specified on thesemi-spherically shaped outer surface of the three-dimensional substrate12′ of the surface acoustic wave device 60 according to the fifthembodiment to be aligned with a line of intersection between at leastone of the plurality of specific crystal faces of the crystal formingthe three-dimensional substrate 12′ and the semi-spherically shapedouter surface thereof, in the same manner as in the case where theoutermost circumferential line 12 b, which serves as a reference forextending the propagation surface zone 12 a continuously, is specifiedon the spherically shaped outer surface of the three-dimensionalsubstrate 12 of the surface acoustic wave device according to the firstembodiment or its modification to be aligned with a line of intersectionbetween at least one of the plurality of specific crystal faces of thecrystal forming the three-dimensional substrate 12 and the sphericallyshaped outer surface thereof. And, the outermost circumferential line12′b is preferably included in the range of the propagating surface zone12′a.

A method for specifying the outermost circumferential line 12′b servingas a reference for extending the propagating surface zone 12′a along theouter surface of the three-dimensional substrate 12′ of the presentembodiment is identical to that for specifying the outermostcircumferential line 12 b on the outer surface of the three-dimensionalsubstrate 12 according to the above-described first embodiment and itsmodification.

In this embodiment, the electro-acoustic transducing element 14 isdirectly formed on the outer surface of the three-dimensional substrate12′ of the present embodiment within the propagating surface zone 12′aso as to propagate the surface acoustic wave along the outermostcircumferential line 12′b in the range of the propagating surface zone12′a while keeping its energy of at least 80% or more, and the abovedescribed electro-acoustic transducing element control unit 20 isconnected to the electro-acoustic transducing element 14.

In this embodiment, a surface acoustic wave reflector 62 is formed at aposition distant from the electro-acoustic transducing element 14 in apropagating direction of the surface acoustic wave, which is excited inthe range of the propagating surface zone 12′a by the electro-acoustictransducing element 14 and which propagates along the outermostcircumferential line 12′b in the range of the propagating surface zone12′a. The surface acoustic reflector 62 reflects the surface acousticwave, which propagates along the propagating surface zone 12′a from theelectro-acoustic transducing element 14 toward the surface acoustic wavereflector 62, to be oriented toward the electro-acoustic transducingelement 14 via the same passage.

Also in this embodiment, a portion of the outer surface other than thepropagating surface zone 12′a may be formed in an arbitrary shape aslong as the propagating surface zone 12′a is specified in accordancewith the predetermined method described above.

In this embodiment, a portion of the three-dimensional substrate 12′other than the propagating surface zone 12′a is supported on a base (notshown).

In this embodiment, the acoustic surface wave, which is excited alongthe propagating surface zone 12′a made of a part of the annular shapedcurved surface by the electro-acoustic transducing element 14 and whichpropagates along the propagating surface zone 12′a without attenuatingsignificantly, changes in response to a variety of changes in a fluid(gas or liquid) including in an outer space that is an environment, withwhich the propagating surface zone 12′a along the outer surface of thethree-dimensional substrate 12′ comes into contact. And, the surfaceacoustic wave device 60 of the present embodiment can detect a change inthe environment, i.e., a difference in the environment, by receiving thechange in the signal, which is generated from the electro-acoustictransducing element 14, in the electro-acoustic transducing elementcontrol unit 20.

Further, in this embodiment, as in the surface acoustic wave device 30of the second embodiment described above with reference to FIG. 6, aplurality of electro-acoustic transducing elements 14, each of whichconnected to the electro-acoustic transducing element control unit 20,can be formed along a plurality of propagating surface zones 12′a alonga plurality of outermost circumferential lines 12′b aligned with aplurality of lines of intersection between a plurality of crystal faces,which are specific to the crystal forming the three-dimensionalsubstrate 12′, and the outer surface thereof, with excludingintersecting portions, at which the plurality of propagating surfacezones 12′a intersect with each other. In this case, the surface acousticwave reflector 62 is mounted at a position opposed to the surfaceacoustic transducing element 14 in each of the plurality of propagatingsurface zones 12′a excluding an intersection portion, with which otherpropagating surface zone 12′a intersects.

Furthermore, in the present embodiment, as in the surface acoustic wavedevice 30 of the second embodiment described above with reference toFIG. 6, it is preferable that, in the case where the three-dimensionalsubstrate 12′ is formed of the Li₂B₄O₇ crystal as described above, thetransmitting and receiving portion of the electro-acoustic transducingelement 14, which is capable to excite the surface acoustic wave alongthe inner surface of the three-dimensional substrate 12′ and topropagate the surface acoustic wave along the inner surface and toreceive the surface acoustic wave propagating along the outer surface,includes a part of the line of intersection (outermost circumferentialline 12′b) on the inner surface of the three-dimensional substrate 12′.With such an arrangement of the transmitting and receiving portion ofthe electro-acoustic transducing element 14, it is possible to improveefficiency of the transmitting and receiving portion of theelectro-acoustic transducing element 14 for exciting and receiving thesurface acoustic wave.

In addition to such an arrangement, in the case where thethree-dimensional substrate 12 is formed of the Li₂B₄O₇ crystal asdescribed above and the outermost circumferential line 12′b is specifiedas shown in FIG. 2, it is more preferable that the transmitting andreceiving portion of the electro-acoustic transducing element 14 isarranged in the band shaped area AA indicating between 75° and 105° inthe arbitrary direction from the above described C axis in order toimprove the above-described efficiency of the transmitting and receivingportion of the electro-acoustic transducing element 14 more remarkably.

Furthermore, as in the surface acoustic wave device 40 of the thirdembodiment described above with reference to FIG. 7, this embodiment canbe modified such that the propagating surface zone 12′a made of at leasta part of the annular curved surface and including the outermostcircumferential line 12′ is specified on, for example, asemi-spherically shaped recessed portion or an inner surface of asemi-spherically shaped cavity formed on or in the three-dimensionalsubstrate 12′, and that the electro-acoustic transducing element 14 andthe surface acoustic wave reflector 62 are mounted along the propagatingsurface zone 12′a so as to be spaced from each other and opposed to eachother along the outermost circumferential line 12′a.

Still furthermore, in the present embodiment, as in the surface acousticwave device 50 of the fourth embodiment described above with referenceto FIGS. 8 and 9, the electro-acoustic transducing element 14 can beformed on the above-described base (not shown) so as to face thepropagating surface zone 12′a with the predetermined gap S therebetween,instead of directly forming the electro-acoustic transducing element 14on the outer surface of the three-dimensional substrate 12′ within thepropagating surface zone 12′a.

Yet furthermore, another electro-acoustic transducing element 14connected to the electro-acoustic transducing element control unit 20described previously can be used instead of the surface acoustic wavereflector 62.

Sixth Embodiment

Hereinafter, a sixth embodiment of the surface acoustic wave deviceaccording to the present invention will be described in detail withreference to FIGS. 11 to 17 included in the accompanying drawings.

FIG. 11 shows an appearance of a surface acoustic wave device 110according to the sixth embodiment. The surface acoustic wave device 110comprises: a three-dimensional substrate 112 having a surface, whichincludes a band shaped propagating surface zone 112 a made of at least apart of a continuous annular curved surface and which is capable topropagate a surface acoustic wave; and an electro-acoustic transducingelement 114, which is capable of exciting the surface acoustic wavealong the propagating surface zone 112 a and propagating the surfaceacoustic wave along the propagating surface zone 112 a and receiving thesurface acoustic wave propagating along the propagating surface zone 112a.

Here, the band shaped propagating surface zone 112 a is drawn such thata dimension in its widthwise direction W is uniform at any points in adirection in which the band shaped propagating surface zone 112 a iscontinuous in the annular shape, in order to simplify the drawing ofFIG. 11. However, in actuality, while the surface acoustic wavepropagates in the direction in which the band shaped propagating surfacezone 112 a is continuous in the annular shape along the surface of thethree-dimensional substrate 112, the dimension of the surface acousticwave in the widthwise direction W may be uniform as shown in FIG. 11 ormay repeatedly diverge and converge.

In any case, it is practically desired that the surface acoustic wavepropagates along the band shaped propagating surface zone 112 a for adesired distance from the electro-acoustic transducing element 114 orper one circulation, while keeping at least 80% or more of energythereof.

In this embodiment, whole of the three-dimensional substrate 112 isformed of a LiNbO₃ crystal of a trigonal system in a spherical shape.Therefore, in this embodiment, the band shaped propagating surface zone112 a is continuous in the annular shape along the spherically shapedsurface of the three-dimensional substrate 112. The band shapedpropagating surface zone 112 a is continuous along an outermostcircumferential line 112 b of the three-dimensional substrate 112, andpreferably, the outermost circumferential line 112 b is included in therange of the band shaped propagating surface zone 112 a.

On the outer surface of the three-dimensional substrate 112, theoutermost circumferential line 112 b, as shown in FIG. 12, coincideswith a line of intersection between one crystal face of the LiNbO₃crystal and the outer surface of the three-dimensional substrate 112, anormal line of the crystal face being a crystal axis CA specified byrotating a +Y axis that is one crystal axis of the LiNbO₃ crystal by 20°in a +Z direction with an X axis being a rotational center. That is, theoutermost circumferential line 112 b along which the band shapedpropagating surface zone 112 a extends along one crystal face of theLiNbO₃ crystal on the outer surface of the three-dimensional substrate112. While the surface acoustic wave propagates along the abovedescribed crystal face on the outer surface of the three-dimensionalsubstrate 112, a large energy diffusion of the surface acoustic wavewill not occur in a direction, which crosses the above crystal face.Thus, the surface acoustic wave can propagate most efficiently along theouter surface of the three-dimensional substrate 112.

The LiNbO₃ crystal forming the three-dimensional substrate 112 is thetrigonal system, and thus, has three crystal axes +Y, which areseparated from each other by 120° in one plane as shown in FIG. 13.Therefore, three outermost circumferential lines 112 b can be specifiedon the spherically shaped outer surface of the three-dimensionalsubstrate 112 formed of the LiNbO₃ crystal, by three lines ofintersection between three crystal faces, each normal line of which iseach of three crystal axes CA specified by rotating each of these threecrystal axes +Y by 20° in the +Z direction with the X axis being arotational center, and the outer surface of the three-dimensionalsubstrate 112. And, three propagating surface zones 112 a, which arecontinuous as described above along the three outermost circumferentiallines 112 b, can be specified on the spherically shaped outer surface ofthe three-dimensional substrate 112 formed of the LiNbO₃ crystal.

On the outer surface of the three-dimensional substrate 112 according tothe sixth embodiment and formed of the LiNbO₃ crystal of the trigonalsystem in the spherical shape, it is also possible to specify theoutermost circumferential line 112 b, along which the propagatingsurface zone 112 a is continuous, as follows.

That is, on the outer surface of the three-dimensional substrate 112,the outermost circumferential line 112 b is, as shown in FIG. 14,aligned with a line of intersection between a crystal face of thethree-dimensional substrate 112 formed of the LiNbO₃ crystal and theouter surface of the three-dimensional substrate 112, a normal line ofthe crystal face being a crystal axis CB specified by rotating the +Yaxis that is one crystal axis of the LiNbO₃ crystal by 26° in a −Zdirection with the X axis being a rotational center. In this case, thismeans that the outermost circumferential line 112 b, along which thepropagating surface zone 112 a extends along the outer surface of thethree-dimensional substrate 112, extends on one crystal face other thanthe above described three crystal faces, each normal line of which isthe crystal axis CA specified by rotating each of the above describedthree +Y axes in the LiNbO₃ crystal by 20° in the +Z direction aroundthe X axis. While a surface acoustic wave propagates along such anothercrystal face on the outer surface of the three-dimensional substrate112, significant diffusion of energy of the surface acoustic wave doesnot occur in a direction intersecting with such another crystal face,thus making it possible to propagate the surface acoustic wave along theouter surface of the three-dimensional substrate 112 most efficiently,as in the above described case where the surface acoustic wavepropagates along each of the above described three crystal faces.

Since the LiNbO₃ crystal forming the three-dimensional substrate 112 isthe trigonal system and has the three crystal axes +Y, which areseparated from each other by 120° in one plane as shown in FIG. 15,other three outermost circumferential lines 112 b can be specified onthe spherically shaped outer surface of the three-dimensional substrate112 formed of the LiNbO₃ crystal, by three lines of intersection betweenthree crystal faces, each normal line of which is each of three crystalaxes CB specified by rotating each of these three crystal axes +Y by 26°in the −Z direction with the X axis being a rotational center, and theouter surface of the three-dimensional substrate 112. And, other threepropagating surface zones 112 a, which are continuous as described abovealong the other three outermost circumferential lines 112 b, can bespecified on the spherically shaped outer surface of thethree-dimensional substrate 112 formed of the LiNbO₃ crystal.

That is, since the LiNbO₃ crystal forming the three-dimensionalsubstrate 112 has a total of six crystal faces, it is possible tospecify a total of six outermost circumferential lines 112 b on theouter surface of the three-dimensional substrate 112 wholly formed ofthe LiNbO₃ crystal.

In addition, it is possible to visually estimate an actual width of thesurface acoustic wave, which propagates along the surface of thethree-dimensional substrate 112, in a direction orthogonal to itspropagating direction along the surface, because, for example, afterdepositing water droplets on the surface, the surface acoustic wave doesnot propagate along a portion of the surface on which water droplets aredeposited.

In general, in a case where a surface acoustic wave having a highfrequency is excited by using a ladder shaped electrode as anelectro-acoustic transducing element, an effective width of the laddershaped electrode (that is, a dimension of a portion of the ladder shapedelectrode, at that portion the ladder shaped electrode enables to excitea surface acoustic wave along the surface of the three-dimensionalsubstrate and to propagate the excited wave in a desired direction andto receive the surface acoustic wave propagating along the surface, in adirection orthogonal to the desired direction along the surface) isreduced. However, it is found that a surface acoustic wave exciting andreceiving efficiency of the effective width of the ladder shapedelectrode is extremely lowered where the effective width is greater than1.5 times of a radius of curvature of a band shaped propagating surfacezone (designated by reference numeral 112 a in FIG. 11) on the outersurface in a direction, which is the above desired direction, orthogonalto an outermost circumferential line (designated by reference numeral112 b in FIG. 11).

Portions of the outer surface of the three-dimensional substrate 112,which are other than the propagating surface zone 112 a along which thesurface acoustic wave excited by the electro-acoustic transducingelement 114 propagates, are supported on a base 118 by supporting arms116. In order to have no effect on the surface acoustic wave propagatingalong the propagating surface zone 112 a, nothing but theelectro-acoustic transducing element 114 is brought into contact withthe propagating surface zone 112 a. Therefore, in the presentembodiment, an electro-acoustic transducing element control unit 120,which is for making the electro-acoustic transducing element 114 toexcite the surface acoustic wave along the propagating surface zone 112a and for receiving a signal from the electro-acoustic transducingelement 114 when the electro-acoustic transducing element 114 receivesthe surface acoustic wave propagating along the propagating surface zone112 a, is connected to the electro-acoustic transducing element 114 bylead wires extending from the electro-acoustic transducing element 114on the portions of the outer surface of the three-dimensional substrate112 other than the propagating surface zone 112 a. The electro-acoustictransducing element control unit 120 comprises, for example, animpedance matching circuit 120 a, a circulator 120 b, an oscillator 120c including a high frequency power supply, an amplifier 120 d, and adigital oscilloscope 120 e, etc. as shown in FIG. 11. A high frequencyradio wave receiving antenna can also be used instead of the oscillator120 c.

As shown in FIG. 16, it is preferable that the electro-acoustictransducing element 114 is configured so that an orientation MD, inwhich a flow density of energy of a surface acoustic wave excited alongthe propagating surface zone 112 a becomes maximum, is within 20° withrespect to the outermost circumferential line 112 b. This angle is morepreferably within 10°, and further preferably within 5°. This meansthat, as long as the surface acoustic wave excited along the propagatingsurface zone 112 a by the electro-surface transducing element 114 cancirculate at a small attenuation rate such that, for example, 80% ormore of energy can be maintained every circulation along the outermostcircumferential line 12 b on the outer surface of the three-dimensionalsubstrate 112, the surface acoustic wave may tends to be diffused fromthe outermost circumferential line 112 b more than a width of thesurface acoustic wave immediately after it is excited, while the surfaceacoustic wave propagates, but it is preferable that the surface acousticwave is excited by the electro-surface transducing element 114 such thatthe orientation MD is within the above described angles.

A phrase “along the outermost circumferential line” described withrespect to the present invention means a case in which, when the surfaceacoustic wave circulates or propagates along a propagation passage, adirection, in which the flow density of energy of the surface acousticwave becomes maximum, is preferably within 20°, more preferably within10°, and further preferably within 5° with respect to the outermostcircumferential line.

In this embodiment, the electro-acoustic transducing element 114 isdirectly formed on the outer surface of the three-dimensional substrate112 within the propagating surface zone 112 a. In this embodiment, theelectro-acoustic transducing element 114 is a ladder shaped electrode122 such as, for example, a comb shaped electrode, and can be directlyformed on the outer surface with a variety of publicly known processessuch as, for example, vapor deposition, printing, sputtering, andsol-gel techniques.

In the case where the electro-acoustic transducing element 114 is formedof the ladder shaped electrode 122, it is preferable that, as well shownin FIG. 17, the ladder shaped electrode 22 is configured so that a lineextending along the outer surface of the three-dimensional substrate 112and being orthogonal to a transmitting and receiving portion (a portionof the above described effective width) of the ladder shaped electrode122 capable of exciting a surface acoustic wave along the propagatingsurface zone 112 a and receiving the surface acoustic wave propagatingalong the propagating surface zone 112 a, is included in a range equalto or smaller than 10° with respect to the outermost circumferentialline 112 b, along which the propagating surface zone 112 a extends. Inmore detail, this means that it is preferable that an orthogonal lineOL, which extends along the outer surface of the propagating surfacezone 112 a and which is orthogonal to the transmitting and receivingportion at each terminal (line element) 122 a in the pattern of theladder shaped electrode 122 [in the case of the ladder shaped electrode122, the transmitting and receiving portion at each terminal (lineelement) 122 a in the pattern of the ladder shaped electrode 122,overlapping each other in a direction along the outermostcircumferential line 112 b], is in a range equal to or smaller than 10°with respect to the outermost circumferential line 112 b.

The reason is identical to the reason why it is preferable that theelectro-acoustic transducing element 114 is configured so that theorientation MD, in which the flow density of energy of the surfaceacoustic wave excited along the propagating surface zone 112 a becomesmaximum, is within 20° with respect to the outermost circumferentialline 112 b, as described previously with reference to FIG. 16.

Further, it is preferable that an arrangement pitch P of the pluralityof terminals 122 a (see FIG. 17) in the pattern of the ladder shapedelectrode 122 in a direction along the outermost circumferential line112 b is equal to or smaller than 1/10 of the radius of curvature of theoutermost circumferential line 112 b. The arrangement pitch P isequivalent to one wavelength (i.e., vibration cycle) of the surfaceacoustic wave excited by the ladder shaped electrode 122.

When the wavelength of the surface acoustic wave (i.e., the arrangementpitch P of the plurality of terminals 122 a in the pattern of the laddershaped electrode 122) is greater than 1/10 of the radius of curvature ofthe outermost circumferential line 112 b included in the propagatingsurface zone 112 a along which the surface acoustic wave propagates (inthe case where the propagating surface zone 112 a is a part of thespherical surface as in this embodiment, the radius of curvature is aradius of the spherical surface), a function of a geometrical feature ofthe curved propagating surface zone 112 a to restrict diffusion of thesurface acoustic wave propagating along the propagating surface zone 112a becomes weak. Therefore, in order to propagate a surface acoustic wavehaving a comparatively long wavelength along the propagating surfacezone 112 a on the surface of the three-dimensional substrate 112 for adesired distance, the radius of curvature of the outermostcircumferential line 112 b included in the propagation surface zone 112a must be preset so as to meet the above-described relationship with theabove wavelength.

Consequently, it is preferable that the arrangement pitch is defined asdescribed above to efficiently propagate a surface acoustic wave alongthe propagating surface zone 112 b.

Inventors of the present invention actually form a spherically shapedthree-dimensional substrate out of the LiNbO₃ crystal in accordance withthis embodiment, and its diameter is 25.4 mm. And, a ladder shapedelectrode to be used as an electro-acoustic transducing element isformed on the outer surface of the spherically shaped three-dimensionalsubstrate at a position corresponding to the +X direction of the abovecrystal viewed from the center of the three-dimensional substrate. Theladder shaped electrode is formed by forming a film on the outer surfaceof the three-dimensional substrate with vapor deposition of 1000angstroms of chrome or vapor deposition of 1000 angstroms of gold, andthen by photolithography processing the film to make terminals (lineelements) in a pattern of the ladder shaped electrode being orthogonalto a direction circulating on the above described spherically shapedouter surface around a direction obtained by rotating the +Y axis of theLiNbO₃ crystal by 20° in the +Z direction with the X axis being as arotational center. An arrangement pitch P of the terminals (lineelements) in the pattern of the ladder shaped electrode formed at thistime is 0.532 mm. And, in the pattern, a width of each terminal (lineelement) is 0.133 mm and a plurality of terminals (line elements) arearranged at intervals of 0.133 mm, respectively. Further, when a desiredpulse voltage is applied between the terminals (line elements) adjacentto each other, an electric field is generated between portions of theadjacent terminals (line elements) overlapping with each other. And, alength of the overlapping portion of each of the adjacent terminals(line elements) is 3.1 mm.

Although the dimensions of the ladder shaped electrode, which is formedon the outer surface of the spherically shaped three-dimensionalsubstrate of the LiNbO₃ crystal by the inventors of the presentapplication and which is used actually as an electro-acoustictransducing element, are described, a ladder shaped electrode made ofany conventionally known material and/or having any dimensions and/orany shape can be used as long as it can achieve required functions ortechnical advantages of the present invention on the outer surface ofthe three-dimensional substrate.

When an impulse signal of 2 nanoseconds in half-value width is appliedat a voltage of 100V to the ladder shaped electrode of the sphericallyshaped surface acoustic wave device configured as described above, it isverified by a digital oscilloscope that a burst signal having a centerfrequency of about 6.5 MHz is repeatedly outputted from theabove-described ladder shaped electrode at least 50 times at intervalsof 21.8 μs in the above described circulating direction. This means thata surface acoustic wave circulates along the outer surface of thespherically shaped three-dimensional substrate of the LiNbO₃ crystalhaving a diameter of 25.4 mm as described above, at least 50 times ormore at an average speed of 3658 m/s in the direction in which thesurface acoustic wave circulates.

The inventors of the present invention form a ladder shaped electrode,which is used as an electro-acoustic transducing element, in a differentway as that described above at the same position as that described aboveon the outer surface of the spherically shaped three-dimensionalsubstrate made of the LiNbO₃ crystal having the diameter equal to thatdescribed above. That is, in this case, the ladder shaped electrode isformed by forming a film on the outer surface of the three-dimensionalsubstrate with vapor deposition of 1000 angstroms of chrome or vapordeposition of 1000 angstroms of gold, and then by photolithographyprocessing the film to make terminals (line elements) in a pattern ofthe ladder shaped electrode being orthogonal to a direction circulatingon the above described spherically shaped outer surface around adirection obtained by rotating the +Y axis of the LiNbO₃ crystal by 26°in the −Z direction with the X axis being as a rotational center.

When an impulse signal is applied in the same manner as described aboveto the ladder shaped electrode of the spherically shaped surfaceacoustic wave device configured as described above, it is verified bythe digital oscilloscope that a burst signal having a center frequencyof about 6.5 MHz is repeatedly outputted from the above-described laddershaped electrode at least 50 times at intervals of 22.5 μs in the abovedescribed circulating direction. This means that a surface acoustic wavecirculates along the outer surface of the spherically shapedthree-dimensional substrate of the LiNbO₃ crystal having the diameter of25.4 mm as described above, at least 50 times or more at an averagespeed of 3540 m/s in the direction in which the surface acoustic wavecirculates.

Then, a water-containing cotton swab is brought into contact with aposition on the outer surface of each of two types of the sphericallyshaped surface acoustic wave devices configured as described above bythe inventors of the present application, the position being distantfrom the ladder shaped electrode in the above described circulatingdirection (i.e., on the circulating passage of the surface acousticwave). As a result, it has been found that, when an impulse signal isapplied to the ladder shaped electrode as described above, no output canbe generated from the ladder shaped electrode and the circulation of thesurface acoustic wave is inhibited. Further, the water-containing cottonswab is brought into contact with a position on the outer surface ofeach of two types of the spherically shaped surface acoustic wavedevices configured as described above, the position being distant fromthe ladder shaped electrode for 5 mm or more in a direction orthogonalto the above circulating direction (i.e., a position detached from thecirculating passage of the surface acoustic wave). As a result, it hasbeen found that, when an impulse signal is applied to the ladder shapedelectrode as described above, a burst signal is repeatedly outputted asdescribed above from the ladder shaped electrode, and the abovedescribed circulation of the surface acoustic wave is not inhibited.

First Modification of Sixth Embodiment

Now, with reference to FIGS. 18 and 19, a first modification of thesixth embodiment of the surface acoustic wave device according to thepresent invention will de described in detail.

In a surface acoustic wave device of this modification, thethree-dimensional substrate 112, which is formed of the LiNbO₃ Crystalof the trigonal system in the sixth embodiment, is formed of a LiTaO₃crystal of the similar trigonal system in the spherical shape.Concurrently, a method for specifying the outermost circumferential line112 b on the outer surface of the three-dimensional substrate 112 isalso different from that in the case of the three-dimensional substrate112 formed of the LiNbO₃ of the trigonal system in the sixth embodiment.However, structural elements other than those described above areidentical to those of the surface acoustic device of the sixthembodiment described previously.

In the surface acoustic wave device of this first modification, theoutermost circumferential line 112 b is aligned with a line ofintersection between one crystal face of the three-dimensional substrate112, which is wholly formed of the LiNbO₃ crystal of the trigonalsystem, and the outer surface of the three-dimensional substrate 112 onthe outer surface, a normal line of the crystal face being a crystalaxis CC specified by rotating is a +Y axis that is one crystal axis ofthe LiTaO₃ crystal by 45° in a −Z direction with an X axis being arotational center, as shown in FIG. 18. And, while the surface acousticwave propagates along such one crystal face along the outer surface ofthe three-dimensional substrate 112, significant diffusion of energy ofthe surface acoustic wave does not occur in a direction intersectingwith the above-described crystal face, thus making it possible topropagate the surface acoustic wave along the outer surface of thethree-dimensional substrate 112 most efficiently, as is the case of thecrystal face of the sixth embodiment.

Since the LiTaO₃ crystal forming the three-dimensional substrate 112 isthe trigonal system, it has three crystal axes +Y separating from eachother for 120° in one plane, as shown in FIG. 19. Therefore, where threelines of intersection specified as described above with respect to thethree crystal axes +Y are defined as three outermost circumferentiallines 112 b, it is possible to specify three propagating surface zones112 a, which are continuous as described above along the three outermostcircumferential lines 112 b.

Second Modification of Sixth Embodiment]

Now, with reference to FIGS. 20 and 21, a second modification of thesixth embodiment of the surface acoustic wave device according to thepresent invention will be described in detail.

In a surface acoustic wave device of this modification, thethree-dimensional substrate 112, which is formed of the LiNbO₃ crystalof the trigonal system in the sixth embodiment, is formed of a quartzcrystal of the similar trigonal system in the spherical shape.Concurrently, a method for specifying the outermost circumferential line112 b on the outer surface of the three-dimensional substrate 112 isalso different from that in the case of the three-dimensional substrate112 formed of the LiNbO₃ of the trigonal system in the sixth embodiment.However, structural elements other than those described above areidentical to those of the surface acoustic device of the sixthembodiment described previously.

In the surface acoustic wave device of this second modification, theoutermost circumferential line 112 b is aligned with a line ofintersection between one crystal face of the three-dimensional substrate112, which is wholly formed of the quartz crystal of the trigonalsystem, and the outer surface of the three-dimensional substrate 112 onthe outer surface, a normal line of the crystal face being a +Y axisthat is one crystal axis CD of the quarts crystal, as shown in FIG. 20.And, while the surface acoustic wave propagates along such one crystalface along the outer surface of the three-dimensional substrate 112,significant diffusion of energy of the surface acoustic wave does notoccur in a direction intersecting with the above-described crystal face,thus making it possible to propagate the surface acoustic wave along theouter surface of the three-dimensional substrate 112 most efficiently,as is the case of the crystal face of the sixth embodiment.

Since the quarts crystal forming the three-dimensional substrate 112 isthe trigonal system, it has three crystal axes +Y separating from eachother for 120° in one plane, as shown in FIG. 21. Therefore, where threelines of intersection specified as described above with respect to thethree crystal axes +Y are defined as three outermost circumferentiallines 112 b, it is possible to specify three propagating surface zones112 a, which are continuous as described above along the three outermostcircumferential lines 112 b.

In the surface acoustic wave devices 110 according to the abovedescribed sixth embodiment, and to its first and second modifications, avariety of dimensions of the three-dimensional substrate 112 and avariety of dimensions of the electro-acoustic transducing element 114are set as follows. That is, the surface acoustic wave excited by theelectro-acoustic transducing element 114 along the outer surface of thethree-dimensional substrate 112 of the surface acoustic wave device 110circulates along the outer surface in a direction, in which thepropagating surface zone 112 a is continuous in an annular shape alongthe outermost circumferential line 112 b specified as described above,within the range of the propagating surface zone 112 a at an energyexhaust rate that is substantially equal to or smaller than 20% per onecirculation (i.e., while keeping 80% or more of energy per onecirculation).

This means that the three-dimensional substrate 112 of the surfaceacoustic wave device 110 may be formed in any arbitrary shape other thanthe propagating surface zone 112 a. For example, the three-dimensionalsubstrate 112 can be formed in a ring-like doughnut shape, a barrelshape, a rugby ball shape, or a disk shape, each having the annularpropagating surface zone 112 a on its outer surface.

In the surface acoustic wave devices 110 according to theabove-described sixth embodiment, and to its first and secondmodifications, when any change occurs in a fluid (gas or liquid) filledin a space, with which the propagating surface zone 112 a comes intocontact (i.e., when any change occurs in an external environment, withwhich the propagating surface zone 112 a comes into contact), a changeoccurs in a propagation speed of the surface acoustic wave propagatingalong the propagating surface zone 112 a or in a propagation time of thesurface acoustic wave required for one circulation. That is, the surfaceacoustic wave device 110 can be used as an environmental differencedetecting apparatus for detecting a change or a difference in anexternal environment.

Seventh Embodiment

Now, a seventh embodiment of the surface acoustic wave device accordingto the present invention will be described in detail with reference toFIG. 22.

In the present embodiment, the electro-acoustic transducing element 114is formed as described above along each of an arbitrary plurality ofpropagating surface zones 122 a (six zones in the sixth embodiment andthree zones in each of its first and second modifications), that can bespecified as described above on the outer surface of thethree-dimensional substrate 112 of the surface acoustic wave device 110according to any of the sixth embodiment and its first and secondmodifications, at a portion not intersecting with the other propagatingsurface zone 122 a. And, each of the electro-acoustic transducingelements 114 is connected to the electro-acoustic transducing elementcontrol unit 120 described above.

Further, in the present embodiment, a support member 132 for supportingthe three-dimensional substrate 112 on any base (not shown) is fixed ata position on the outer surface of the three-dimensional substrate 112excluding the plurality of propagating surface zones 112 a, along whichthe electro-acoustic transducing elements 114 are formed.

A surface acoustic wave device 130 according to the seventh embodimentand configured as described above is superior to the surface acousticwave device 100 according to any of the sixth embodiment and its firstand second modifications, when they are used as environmental differencedetecting apparatuses.

The reason is as follows.

In the case where, as in the above-described surface acoustic wavedevice 110, only one electro-acoustic transducing element 114 and oneelectro-acoustic transducing element control unit 120 connected heretoare used, a slight change occurs in a propagation speed of the surfaceacoustic wave propagating along the propagating surface zone 112 a or ina propagation time of the surface acoustic wave required for onecirculation, when any physical change occurs in the surface acousticwave element 110 due to an effect of the change in the above describedexternal environment (for example, an expansion or a contraction of thethree-dimensional substrate 112 due to a temperature change in theexternal environment).

Consequently, in order to more precisely detect a change in a fluid (gasor liquid) filled in a space, with which the propagating surface zone112 a comes into contact as described previously, a physical change ofthe surface acoustic wave device 11 due to the effect of the change inthe external environment described above must be considered.

The surface acoustic wave device 130 according to the seventh embodimentdescribed with reference to FIG. 22 is configured so that at least oneof the plurality of propagating surface zones 112 a, along which theelectro-acoustic transducing elements 114 are formed along the outersurface of the three-dimensional substrate 112, is isolated from anexternal environment, a change of which is to be detected, and that atleast another of the plurality of propagating surface zones 112 a, alongwhich the electro-acoustic transducing elements 114 are formed, isbrought into contact with the external environment.

With such a configuration, a signal generated from the electro-acoustictransducing element 114 along the propagating surface zone 112 a, whichis isolated from the external environment, and received by theelectro-acoustic transducing element control unit 120 corresponding tothe above described electro-acoustic transducing element 114, indicatesa physical change of the surface acoustic wave device 110 due to thechange in the external environment. In addition, a signal generated fromthe electro-acoustic transducing element 114 along the propagatingsurface zone 112 a, which is in contact with the external environment,and received by the electro-acoustic transducing element control unit 20corresponding to the above described electro-acoustic transducingelement 114, indicates a change in the external environment, togetherwith the physical change of the surface acoustic wave device 110, due tothe change in external environment.

Accordingly, by subtracting the signal, which is generated from theelectro-acoustic transducing element 114 along the propagating surfacezone 112 a isolated from the external environment and which is receivedby the electro-acoustic transducing element control unit 120corresponding to the electro-acoustic transducing element 114, from thesignal, which is generated from the electro-acoustic transducing element114 along the propagating surface zone 112 a come into contact with theexternal environment and which is received by the electro-acoustictransducing element control unit 120 corresponding to theelectro-acoustic transducing element 114, it possible to purely detectonly the change in the external environment.

Modification of Seventh Embodiment

FIG. 23 shows a modification of the surface acoustic wave deviceaccording to the seventh embodiment described above with reference toFIG. 22.

In this modification, a common electro-acoustic transducing element 114′for exciting surface acoustic waves, which is common to a plurality ofpropagating surface zones 112 a, is formed at an intersecting region ofthe propagating surface zones 112 a on the outer surface of thethree-dimensional substrate 112. The common electro-acoustic transducingelement 114′ is connected to a common electro-acoustic element controlunit 120′, and the common electro-acoustic element control unit 120′controls the common electro-acoustic transducing element 114′ so as toexcite and propagate surface acoustic waves having the same frequencyeach other along the plurality of propagating surface zones 112 a at thesame time.

Further, an electro-acoustic transducing element 114″ for receiving asurface acoustic wave, is formed along each of the plurality ofpropagating surface zones 112 a at a position, which does not overlapwith the other propagating surface zone. Each of the plurality ofelectro-acoustic transducing elements 114″ for receiving is connected toa receiving electro-acoustic transducing element control unit 120″, andis further connected to a signal difference detecting means 24 via therespective receiving electro-acoustic transducing element control unit120″, the signal difference detecting means 24 detecting a differencebetween signals received by the respective electro-acoustic transducingelement control units 120″.

Normally, the plurality of receiving electro-acoustic transducingelements 114″ receive surface acoustic waves from the plurality ofpropagating surface zones 112 a at the same time. However, for example,when a foreign matter such as a liquid comes into contact with each ofthe propagating surface zones 112 a due to a change in an environment ina part of an external space adjacent to the each of the propagatingsurface zones 112 a, a difference occurs between a propagation speed ofa surface acoustic wave along the each of the propagating surface zones112 a, with which such a foreign matter comes into contact, and apropagation speed of a surface acoustic wave in each of the remainingplural propagating surface zones 112 a, with which no foreign mattercomes into contact. Due to this difference, the signal differencedetecting means 124 connected to the plurality of receivingelectro-acoustic transducing elements 114″ via the plurality ofreceiving electro-acoustic transducing element control units 120″ candetect a degree of a change in the environment in the part of the aboveexternal space.

In this modification, one common excitation electro-acoustic transducingelement 114′ and the plurality of receiving electro-acoustic transducingelements 114″ are formed with respect to the plurality of propagatingsurface zones 112 a. Thus, the one common excitation electro-acousticelement control unit 120′ is provided for the one common excitationelectro-acoustic transducing element 114′, and the plurality ofreceiving electro-acoustic transducing element control units 120″ areprovided for the plurality of receiving electro-acoustic transducingelements 114″.

A circuit design for the common excitation electro-acoustic elementcontrol unit 120′ and that for each of the plurality of receivingelectro-acoustic transducing element control units 120″ in thismodification are much easier as compared with a circuit design for eachof the plurality of electro-acoustic transducing element control units120 provided for the plurality of transmitting and receivingelectro-acoustic transducing elements 114 formed along the plurality ofpropagating surface zones 112 a in the seventh embodiment shown in FIG.22.

Eighth Embodiment

Now, an eighth embodiment of the surface acoustic wave element accordingto the present invention will be described in detail with reference toFIG. 24.

A three-dimensional substrate 112 of a surface acoustic wave device 140according to the eighth embodiment has a recessed or hollow portion, andthe recessed portion or an inner surface 112 c of the hollow portionincludes a propagating surface zone 112 a, which is a curved surfacebeing continuous in an annular shape and along which a surface acousticwave can propagate. FIG. 24 shows the three-dimensional substrate 112having a through hole that is one kind of the hollow portion.

A whole of the three-dimensional substrate 112 is formed of a LiNbO₃crystal, a LiTaO₃ crystal, or a quartz crystal, as the three-dimensionalsubstrate 112 according to each of the sixth embodiment and its first orsecond modifications. And, at least one outermost circumferential line112 b is specified on the inner surface of the three-dimensionalsubstrate 112 of the surface acoustic wave device 140 according to theeighth embodiment along a line of intersection between one of aplurality of crystal faces, which are particular to a kind of thecrystal forming the three-dimensional substrate 112 of the surfaceacoustic wave device 140 according to the eighth embodiment, and theinner surface of the three-dimensional substrate 112, the outermostcircumferential line 112 b serving as a reference for extending thepropagating surface zone 112 a along the inner surface. Such aspecifying manner of the at least one outermost circumferential line 112b on the inner surface of the three-dimensional substrate 112 is thesame as that of the outermost circumferential line 112 b on the outersurface of the three-dimensional substrate 112 according to each of thesixth embodiment and its first and second modifications, in which theoutermost circumferential line 112 b is specified along the line ofintersection between one of the plurality of crystal faces, which areparticular to the kind of the crystal forming the three-dimensionalsubstrate 112 according to each of the sixth embodiment and its firstand second modifications, and the outer surface of the three-dimensionalsubstrate 112, the outermost circumferential line 112 b serving as areference for extending the propagating surface zone 112 a along theouter surface. Consequently, the propagating surface zone 112 a isspecified along the inner surface so as to extend continuously along theoutermost circumferential line 112 b. The specifying manner of thepropagating surface zone 112 a along the inner surface of thethree-dimensional substrate 112 according to this embodiment is the sameas that of the propagating surface zone 112 a along the inner surface ofthe three-dimensional substrate 112 according to each of the abovedescribed sixth embodiment and its first and second modifications.Therefore, the outermost circumferential line 112 b is preferablyincluded in the range of the propagating surface zone 112 a along theinner surface.

Also in the propagating surface zone 112 a along the inner surface ofthe three-dimensional substrate 12 of this embodiment, theelectro-acoustic transducing element 114 is formed so as to propagatethe surface acoustic wave along the outermost circumferential line 112 bin the range of the propagating surface zone 112 a without significantlyattenuating it, and the above described electro-acoustic transducingelement control unit is connected to the electro-acoustic transducingelement 114.

In this embodiment as well, a portion of the inner surface other thanthe propagating surface zone 112 a may be formed in an arbitrary shapeas long as the propagating surface zone 112 a is specified in accordancewith the above described predetermined manner.

In this embodiment, the acoustic surface wave, which is excited alongthe propagating surface zone 112 a by the electro-acoustic transducingelement 114 and which propagates along the propagating surface zone 112a while keeping its energy of, for example, 80% or more per onecirculation without significant attenuation, changes in response to avariety of changes in a fluid (gas or liquid) passing through theinternal space of a through hole that is an environment, with which thepropagating surface zone 112 a along the inner surface of thethree-dimensional substrate 112 comes into contact. And, the surfaceacoustic wave device 140 of the present embodiment can detect a changein the environment, i.e., a difference in the environment, by receivingthe change in the signal, which is generated from the electro-acoustictransducing element 114, in the electro-acoustic transducing elementcontrol unit 120.

Further, in this embodiment, as in the surface acoustic wave device 130of the seventh embodiment described above with reference to FIG. 22, aplurality of electro-acoustic transducing elements 114, each of which isconnected to an electro-acoustic transducing element control unit 120,can be formed along a plurality of propagating surface zones 112 a alonga plurality of outermost circumferential lines 12 b aligned with aplurality of lines of intersection between a plurality of crystal faces,which are specific to the crystal forming the three-dimensionalsubstrate 112, and the inner surface, with excluding intersectingportions, at which the plurality of propagating surface zones 112 aintersect with each other. With this configuration, as in the surfaceacoustic wave device 130 of the seventh embodiment described above withreference to FIG. 22, the surface acoustic device can be used as anenvironmental difference detecting apparatus, which is capable ofdetecting an environmental difference more precisely.

More further, in this embodiment, as in the surface acoustic wave device130 of the modification of the seventh embodiment described above withreference to FIG. 23, a common excitation electro-acoustic transducingelement 114′ can be formed along the outer surface of thethree-dimensional substrate 112 at an intersection region of a pluralityof propagating surface zones 112 a along a plurality of outermostcircumferential lines 12 b aligned with a plurality of lines ofintersection between a plurality of crystal faces, which are specific tothe crystal forming the three-dimensional substrate 112, and the outersurface thereof, the common excitation electro-acoustic transducingelements 114′ being used for the plurality of propagating surface zones112 a in common. And, at the same time, a plurality of receivingelectro-acoustic transducing elements 114″ can be formed along theplurality of propagating surface zones 112 a excluding the intersectionregion. With this configuration, as in the surface acoustic wave device130 of the modification of the seventh embodiment described above withreference to FIG. 23, the surface acoustic device can be used as anenvironmental difference detecting apparatus, which is capable ofdetecting an environmental difference more precisely.

Ninth Embodiment

Now, a ninth embodiment of the surface acoustic wave device according tothe present invention will be described in detail with reference toFIGS. 25 and 26.

A surface acoustic wave device 150 according to the ninth embodimentcomprises a spherically shaped three-dimensional substrate 112, a wholeof which is formed of a LiNbO₃ crystal, a LiTaO₃ crystal, or a quartzcrystal, as in the three-dimensional substrate 112 according to each ofthe above-described sixth embodiment and its first or secondmodifications. On an outer surface of the three-dimensional substrate112, at least one of a plurality of lines of intersection between aplurality of crystal faces of the material of the three-dimensionalsubstrate 112 and the outer surface thereof, is defined as the outermostcircumferential line 112 b, and the propagating surface zone 112 a isspecified along the outermost circumferential line 112 b so as to becontinuous in an annular shape. The propagating surface zone 112 a alongthe outer surface of the three-dimensional substrate 112 of the surfaceacoustic wave device 150 according to this embodiment also preferablyincludes the outermost circumferential line 112 b in the range of thepropagating surface zone 112 a, as in the propagating surface zone 112 aalong the outer surface of the three-dimensional substrate 112 accordingto each of the above-described sixth embodiment and its first or secondmodifications.

The surface acoustic wave device 150 of the present embodiment isdifferent from the surface acoustic wave device 110 according to each ofthe sixth embodiment and its first and second modifications in that theelectro-acoustic transducing element 114, which is capable of exciting asurface acoustic wave along the propagating surface zone 112 a along theouter surface of the three-dimensional substrate 112 and propagating theexcited surface acoustic wave along the outermost circumferential line112 b in the range of the propagating surface zone 112 a, is notdirectly formed in the propagating surface zone 112 a on the outersurface of the three-dimensional substrate 112.

In this embodiment, a base 152 for supporting a portion of the outersurface of the three-dimensional substrate 112 other than thepropagating surface zone 112 a has a propagating surface zone facingregion 152 a, which faces the propagating surface zone 112 a with apredetermined gap S therebetween, and the electro-acoustic transducingelement 114 is formed in the propagating surface zone facing region 152a of the base 152. The dimensions of the electro-acoustic transducingelement 114 and the arrangement of the electro-acoustic transducingelement 114 with respect to the propagating surface zone 112 a areidentical to those in the case where the electro-acoustic transducingelement 114 is directly formed in the propagating surface zone 112 a ofthe surface acoustic wave device according to each of the sixthembodiment and its first and second modifications.

In the case where the electro-acoustic transducing element 114 is aladder shaped electrode 122 such as a comb shaped electrode, it ispreferable that the predetermined gap S is equal to or smaller than ¼ ofan arrangement pitch P (refer to FIG. 17) of a plurality of lineelements (terminals) in a pattern of the ladder shaped electrode 122.When the predetermined gap S is greater than ¼ of the arrangement pitchP (refer to FIG. 17), it becomes difficult for the electro-acoustictransducing element 114 to always reliably excite a desired surfaceacoustic wave along the propagating surface zone 112 a along the outersurface of the three-dimensional substrate 112.

The surface acoustic wave device 150 according to the ninth embodimentcan be used in the same manner as that in the three-dimensionalsubstrate 112 of each of the sixth embodiment and its first or secondmodifications. Moreover, in the case where the electro-acoustictransducing element 114 faces the propagating surface zone 112 a alongthe outer surface of the three-dimensional substrate 112 with thepredetermined gap S therebetween, an adverse effect, which may begenerated by the electro-acoustic transducing element 114 directlyformed in the propagating surface zone 112 a on the outer surface of thethree-dimensional substrate 112 and which may very slightly affect thesurface acoustic wave excited along the propagating surface zone 112 aand propagating along the propagating surface zone 112 a, can beeliminated. Consequently, a change in the surface acoustic wavepropagating along the propagating surface zone 112 a can be detectedmore precisely.

Further, also in the surface acoustic wave device 150 according to theninth embodiment, as in the modification of the seventh embodimentdescribed above with reference to FIG. 23, the propagating surface zonefacing region 152 a of the base 152 can be faced an intersecting regionof a plurality of propagating surface zones 112 a along a plurality ofoutermost circumferential lines 112 b that can be specified on the outersurface of the three-dimensional substrate 112. In addition, a commonexcitation electro-acoustic transducing element 114′ can be formed onthe propagating surface zone facing region 152 a so as to face theabove-described intersecting region of the plurality of propagatingsurface zones 112 a along the outer surface of the three-dimensionalsubstrate 112 with a predetermined gap S therebetween. Further, apropagating surface zone facing region of an additional base similar tothe base 152 having the propagating surface zone facing region 152 a canbe faced each of the plurality of propagating surface zones 112 a otherthan the above-described intersecting region. In addition, a receivingelectro-acoustic transducing element 114″ can be formed on thepropagating surface zone facing region of the additional base so thatthe receiving electro-acoustic transducing element 114″ faces each ofthe plurality of propagating surface zones 112 a along the outer surfaceof the three-dimensional substrate 112 other than the above-describedintersecting region with a predetermined gap S therebetween. Also inthis case, the surface acoustic device configured as described above canbe used as an environmental difference detecting apparatus capable ofmore precisely detecting an environmental difference, as in the surfaceacoustic wave device 130 according to the modification of the seventhembodiment described previously with reference to FIG. 23.

Tenth Embodiment

Now, a tenth embodiment of a surface acoustic wave device according tothe present invention will be described in detail with reference to FIG.27.

A surface acoustic wave device 160 according to the tenth embodimentcomprises a three-dimensional substrate 112′ having a semisphericalshape, and an outer surface of the three-dimensional substrate 112′includes a propagating surface zone 112′a made of at least a part of acontinuous annular curved surface along which a surface acoustic wavecan propagate.

A whole of the semi-spherically shaped three-dimensional substrate 112′is formed of a LiNbO₃ crystal, a LiTaO₃ crystal, or a quartz crystal, asthe three-dimensional substrate 112 according to each of the sixthembodiment and its first and second modification. At least one outermostcircumferential line 112′b serving as a reference for extending thepropagating surface zone 112′a along a line of intersection between atleast one of a plurality of crystal faces, which are specific to a kindof crystal forming the three-dimensional substrate 112′ of the surfaceacoustic wave device 160 according to the tenth embodiment, and theouter surface thereof is specified on the outer surface of thethree-dimensional substrate 112′, in the same manner as in the casewhere the outermost circumferential line 112 b serving as the referencefor extending the propagating surface zone 112 a along the line ofintersection between at least one of a plurality of crystal faces, whichare specific to a kind of crystal forming the three-dimensionalsubstrate 112 of each of the above described sixth embodiment and itsfirst and second modifications, and the outer surface thereof isspecified on the outer surface of the three-dimensional substrate 112.And, the outermost circumferential line 112′b is preferably included inthe range of the propagating surface zone 112′a.

A method for specifying the outermost circumferential line 112′b servingas the reference for extending the propagating surface zone 112′a alongthe outer surface of the three-dimensional substrate 112′ of thisembodiment is identical to that for specifying the outermostcircumferential line 112 b on the outer surface of the three-dimensionalsubstrate 112 according to each of the above-described sixth embodimentand its first or second modifications.

Further, the electro-acoustic transducing element 114 is directly formedin the propagating surface zone 112′a on the outer surface of thethree-dimensional substrate 112′ of the present embodiment so as topropagate the surface acoustic wave along the outermost circumferentialline 112′b in the range of the propagating surface zone 112′a along theouter surface of the three-dimensional substrate 112′ of the presentembodiment while keeping its energy of, for example, 80% or more per onecirculation, and the above described electro-acoustic transducingelement control unit 120 is connected to the electro-acoustictransducing element 114.

In this embodiment, a surface acoustic wave reflector 162 is formed at aposition distant from the electro-acoustic transducing element 114 in apropagation direction of a surface acoustic wave which is excited in therange of the propagating surface zone 112′a by the electro-acoustictransducing element 114 and which propagates along the outermostcircumferential line 112′b in the range of the propagating surface zone112′a. The surface acoustic wave reflector 162 reflects the surfaceacoustic wave propagated from the electro-acoustic transducing element114 toward the surface acoustic wave reflector 162 along the propagatingsurface zone 112′a so as to return the electro-acoustic transducingelement 114 along the propagating surface zone 112′a in the samepassage.

Also, in this embodiment, a portion of the outer surface other than thepropagating surface zone 112′a may be formed in an arbitrary shape aslong as the propagating surface zone 112′a is specified in accordancewith the predetermined method described previously.

Further, in this embodiment, a portion of the three-dimensionalsubstrate 112′ other than the propagating surface zone 112′a issupported on a base not shown.

In this embodiment, the acoustic surface wave, which is excited alongthe propagating surface zone 112′a made of a part of the annular shapedcurved surface by the electro-acoustic transducing element 114 and whichpropagates along the propagating surface zone 112′a without attenuatingsignificantly, changes in response to a variety of changes in a fluid(gas or liquid) including in an outer space that is an environment, withwhich the propagating surface zone 112′a along the outer surface of thethree-dimensional substrate 112′ comes into contact. And, the surfaceacoustic wave device 160 of the present embodiment can detect a changein the environment, i.e., a difference in the environment, by receivingthe change in the signal, which is generated from the electro-acoustictransducing element 114, in the electro-acoustic transducing elementcontrol unit 120.

Further, in this embodiment, as in the surface acoustic wave device 130of the seventh embodiment described above with reference to FIG. 22, aplurality of electro-acoustic transducing elements 114, each of which isconnected to the electro-acoustic transducing element control unit 120,can be formed along a plurality of propagating surface zones 112′a alonga plurality of outermost circumferential lines 112′b aligned with aplurality of lines of intersection between a plurality of crystal faces,which are specific to the crystal forming the three-dimensionalsubstrate 112′, and the outer surface thereof, with excludingintersecting portions, at which the plurality of propagating surfacezones 112′a intersect with each other. In this case, the surfaceacoustic wave reflector 162 is mounted at a position opposed to thesurface acoustic transducing element 114 in each of the plurality ofpropagating surface zones 112′a excluding an intersection portion, withwhich other propagating surface zone 112′a intersects.

Further, in the present embodiment, as in the surface acoustic wavedevice 130 of the modification of the seventh embodiment described abovewith reference to FIG. 23, a common excitation electro-acoustictransducing element 114′ can be formed at an intersection region of theplurality of propagating surface zones 112′a along the outer surface ofthe three-dimensional substrate 112′. At the same time, a receivingelectro-acoustic transducing element 114″ can be formed along each ofthe plurality of propagating surface zones 112′a excluding theintersection region, instead of the surface acoustic wave reflector 162.

Furthermore, as in the surface acoustic wave device 140 of the eighthembodiment described above with reference to FIG. 24, this embodimentcan be modified such that the propagating surface zone 112 a made of atleast a part of the annular curved surface and including the outermostcircumferential line 112 b is specified on, for example, asemi-spherically shaped recessed portion or an inner surface of asemi-spherically shaped cavity formed on or in the three-dimensionalsubstrate 112, and that the electro-acoustic transducing element 114 andthe surface acoustic wave reflector 162 are mounted along thepropagating surface zone 112 a so as to be spaced from each other andopposed to each other along the outermost circumferential line 112 a.

Still furthermore, in the present embodiment, as in the surface acousticwave device 150 of the ninth embodiment described above with referenceto FIGS. 25 and 26, the electro-acoustic transducing element 114 can beformed on the above-described base (not shown) so as to face thepropagating surface zone 112′a with the predetermined gap Stherebetween, instead of directly forming the electro-acoustictransducing element 114 in the propagating surface zone 112′a of thethree-dimensional substrate 112′.

Alternatively, the common excitation electro-acoustic transducingelement 114′ can be formed on the above-described base (not shown) so asto face the intersection region of the plurality of propagating surfacezones 112′a along the outer surface of the electro-acoustic transducingthree-dimensional substrate 112′, and, at the same time, the receivingelectro-acoustic transducing element 114″ can be formed on theabove-described base (not shown) excluding the intersection region so asto face each of the propagating surface zone 112′a with thepredetermined gap S therebetween, instead of directly forming theelectro-acoustic transducing three-dimensional substrate 112′ element114 in the propagating surface zone 112′a of the three-dimensionalsubstrate 112′.

Yet furthermore, another electro-acoustic transducing element 114connected to the electro-acoustic transducing element control unit 120described previously can be used instead of the surface acoustic wavereflector 162.

A surface acoustic wave device is used as a delay line, an oscillatorelement, a resonator element, a frequency selector element, for example,as a part of an environmental difference detecting apparatus fordetecting a variety of environmental differences, the detectingapparatus including a chemical sensor, a biological sensor, and apressure sensor, or alternatively, as a remote tag, etc.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A surface acoustic wave device, comprising: a three-dimensionalsubstrate having a surface, which includes at least a part of an annularcurved surface formed with a continuous curved surface enabling topropagate a surface acoustic wave; and an electro-acoustic transducingelement, which excites the surface acoustic wave along the surface,which propagates the surface acoustic wave along the surface, and whichenables to receive the surface acoustic wave propagating along thesurface, wherein the three-dimensional substrate is made of a Li₂B₄0₇crystal, and, along the surface of the three-dimensional substrate, theelectro-acoustic transducing element propagates the excited surfaceacoustic wave along a line of intersection between a crystal face of theLi₂B₄0₇ crystal and the surface thereof, a normal line of the crystalface extending in a direction orthogonal to a C crystal axis of theLi₂B₄0₇ crystal, and the line of intersection defined as an outermostcircumferential line of the surface.
 2. A surface acoustic deviceaccording to claim 1, wherein the surface of the three-dimensionalsubstrate has at least a part of a spherical surface.
 3. A surfaceacoustic device according to claim 2, wherein a transmitting andreceiving portion of the electro-acoustic transducing element, whichexcites the surface acoustic wave along the surface of thethree-dimensional substrate, which propagates the surface acoustic wavealong the surface, and which enables to receive the surface acousticwave propagating along the surface, is arranged to the surface of thethree-dimensional substrate to include a part of the line ofintersection.
 4. A surface acoustic device according to claim 1,wherein, on the surface, a curved surface, which enables to propagatethe surface acoustic wave, is continuous in an annular shape, and theelectro-acoustic transducing element excites the surface acoustic wavealong the surface and propagates and circulates the surface acousticwave along the line of intersection.
 5. A surface acoustic deviceaccording to claim 4, wherein the surface of the three-dimensionalsubstrate is a spherical surface.
 6. A surface acoustic device accordingto claim 5, wherein a transmitting and receiving portion of theelectro-acoustic transducing element, which excites the surface acousticwave along the surface of the three-dimensional substrate, whichpropagates the surface acoustic wave along the surface, and whichreceives the surface acoustic wave propagating along the surface, isarranged to the surface of the three-dimensional substrate to include apart of the line of intersection.
 7. A surface acoustic device accordingto claim 1, wherein, in a direction intersecting with an extendingdirection of the line of intersection along the surface, theelectro-acoustic transducing element excites the surface acoustic wavealong the surface and propagates the excited surface acoustic wave alongthe line of intersection while keeping energy of the surface acousticwave by 80% or more per one circulation, and a dimension of theelectro-acoustic transducing element, which enables to receive thesurface acoustic wave, is equal to or smaller than 1/1.5 of a radius ofcurvature of a curved surface extending in a direction orthogonal to theline of intersection on the surface.
 8. A surface acoustic deviceaccording to claim 7, wherein the electro-acoustic transducing elementis arranged along the surface so that an orientation, in which a flowdensity of energy of a surface acoustic wave emitted from theelectro-acoustic transducing element along the line of intersectionbecomes maximum, is equal to or smaller than 20° with respect to theline of intersection corresponding thereto.
 9. A surface acoustic deviceaccording to claim 1, wherein the electro-acoustic transducing elementis formed along a propagating surface zone of the surface of thethree-dimensional substrate, along which the surface acoustic wavepropagates.
 10. A surface acoustic device according to claim 1, whereinthe electro-acoustic transducing element comprises a ladder shapedelectrode, and the ladder shaped electrode is configured so that a line,which is along the surface and orthogonal to a transmitting andreceiving portion in each of a plurality of terminals of the laddershaped electrode, the transmitting and receiving portion enabling toexcite the surface acoustic wave along the surface and to receive thesurface acoustic wave propagating along the surface, is included in arange equal to or smaller than 10° with respect to the line ofintersection corresponding thereto.
 11. A surface acoustic deviceaccording to claim 10, wherein an arrangement pitch of the plurality ofterminals of the ladder shaped electrode in a direction along the lineof intersection is equal to or smaller than 1/10 of a radius ofcurvature of the line of intersection.
 12. A surface acoustic deviceaccording to claim 1, wherein the surface of the three-dimensionalsubstrate is an outer surface of the three-dimensional substrate.
 13. Asurface acoustic device according to claim 1, wherein thethree-dimensional substrate has a recessed portion or hollow portion,and the surface is the recessed portion or an inner surface of thehollow portion of the three-dimensional substrate.
 14. An environmentaldifference detecting apparatus, wherein, along the surface of thesurface acoustic wave device according to claim 1 to 6, a plurality ofelectro-acoustic transducing elements excite surface acoustic waves,propagate the surface acoustic waves along a plurality of lines ofintersection of the surface of the surface acoustic wave device, andreceive the propagated surface acoustic waves to output receptionsignals; the reception signals outputted from the plurality ofelectro-acoustic transducing elements are compared with each other; andan environmental difference in a plurality of portions of a space, withwhich the plurality of portions along the surface propagating theplurality of surface acoustic waves come into contact, is detected.